Storage Performance Benchmarking Q&A – Take 2

J Metz

Our recent Ethernet Storage Forum Webcast, “Storage Performance Benchmarking: Part 2,” has already been viewed by more than 500 people. If you haven’t seen it yet, it’s now available on –demand. Our expert presenters, Ken Cantrell and Mark Rogov did a great job fielding questions during the live event, but of course there wasn’t time to get to them all. So, as promised here are their answers to all of them. If you have additional questions or thoughts, please comment on this blog and we’ll get back to you as soon as we can.

Q: “As an example, am I right to presume workloads are generated by VMs”

A: Ken: It is probably a good idea at this point to define a workload, since we continue to use the term. At a very high level, think of a workload as the mix of operations issued by an application related to the accessing of data. In our case, data stored or made available by a storage solution. With that in mind, absolutely, workloads can be generated by VMs. But they don’t have to be. In other words, “it depends.”

For example, consider these 3 cases:

1) If your SUT (solution under test) was just a simple laptop with no hypervisor and a traditional OS, then there would be no VM in the mix. Your workload would be generated by the application you were measuring (whether that was a simple file copy or something complex like a local database installation).

2) Your SUT is composed of a physical client (like the laptop above) attached to a machine with a hypervisor installed on it and a local guest OS installation that is capable of exporting NFS or SMB shares. The laptop sends I/O via Ethernet to the guest OS. In this example, there is a VM, but it is acting as the storage system, not the workload generator.

3) Now reverse the I/O of example 2. Have the laptop export an SMB share and have the guest OS issue I/Os to that share. Now you finally have VMs generating workloads.

A: Mark: If one examines the solution under test (SUT), and considers the general data flow, then the workload is generated by the clients/hosts layer. Yes, we indicated that the clients/hosts can be VMs, but they also could be physical systems, and, in the case of a SUT consisting of just one laptop, the workload is generated by the application.

Q: Are you going to get around to file performance benchmarking? This infrastructure stuff is not new to me. I have done block all my life, I am interested in stuff about file.

A: Ken: That’s the plan. We are still working out the exact sequence, timing and content for future presentations, but had a dedicated section on both block and file on the original roadmap. If you have specific topics within “file” that you’d like covered, respond in the comments. No promises to cover them, but knowing the desires of the audience is always a good thing.

Keep in mind the intention of the webcast series – lay a strong, but simple foundation, for storage performance fundamentals and then build on that foundation.

A: Mark: The main intent of the series is to lay down basic performance principles first, then build on them to go to more complex topics. Both Ken and I refer to ourselves as “File Heads” and we can’t wait to concentrate on just file, but it would only make sense given that the infrastructure foundations are firm and understood by our audience.

Q: Why doesn’t SPEC SFS have performance testing for such failure models?

A: Ken: Brighttalk provided this comment in isolation, so it isn’t entirely clear which failure models you’re asking for.  I’m assuming you mean a failure like a drive or controller failure. With that assumption, that said, the SFS subcommittee welcomes publications that illustrate a failure condition. SPEC SFS 2014 provides an excellent opportunity for someone to publish once in a non-failure scenario and then again in a failure condition of some sort – as long as that failure condition doesn’t violate any of the run rules regarding stable storage and the failure condition doesn’t generate user visible errors.

Note that SPEC SFS 2014 doesn’t mandate any demonstration of failure scenarios. We’ve discussed this in the past, but it has never been a priority for those that participate in SPEC (which is open to all – see http://www.spec.org for instructions on how to join the SPEC Open Systems Group).

Q: Why is write cache turned off for enterprise drives?

A: Ken: I knew this question was coming. :) This is related to “stable storage” – the guarantee from your storage provider that data they say is safely stored on disk is actually stored on disk. I should clarify that the comment is a little dated and refers to caches designed around volatile memory; this wouldn’t apply to a hybrid SSD/spinning media drive that used the SSD to cache/stage data, since SSDs are non-volatile.

Consider the failure scenario where the enterprise drive has write caching enabled and then experiences a power failure. In most every system sold, the storage controller treats drives pretty much as black boxes – they tell the drive to read or write data at a certain location and expect the drive to do as told. So, when the drive says “yup, I got that data, you’re good!” the storage solution trusts the drive and, when it doesn’t need it in memory any longer, throws it away (that data is safely stored on disk, so this is ok). If the drive chose to cache that information in volatile memory, and loses power, the information is gone.

Midrange and enterprise storage vendors often (I think I can say generally) provide some sort of battery backup in case of power failures. These battery units keep power to at least some of the drives – but remember that drives (especially spinning ones) suck down a lot of power, and often the implementation chooses to keep power only to certain drives that the storage controller uses to flush its own volatile memory structures to.

A quick Internet search shows some specific comments on this topic:

From Seagate (http://knowledge.seagate.com/articles/en_US/FAQ/187751en):

Windows 2000 Professional / Server, Windows XP Home / Professional, Windows Vista and Windows 7 have a nifty little feature called write caching buried within the depths of property tabs. Normally, this type of feature is used with SCSI drives in server applications to provide greater data integrity.

When drives employ write-back cache, any interruption of power to the drive or system may cause lost or corrupted data because the drive does not have time to write the cached data to the disk before the power is lost. However, when write cache is turned off, drive performance slows down.

From Microsoft (https://support.microsoft.com/en-us/kb/259716):

…In addition, enabling disk write caching may increase operating system performance. This article describes how to enable or disable disk write caching…

NOTE: Enabling write caching generates the following warning. This is normal:

By enabling write caching, file system corruption and/or data loss could occur if the machine experiences a power, device or system failure and cannot be shutdown properly.

Q: What’s the difference between CPU and ASIC? When to use which word?

A: Ken: Unfortunately, the SNIA dictionary doesn’t define either term. At the easiest level, both are acronyms. CPU = central processing unit, and ASIC = application specific integrated circuit. At the next level, think of a CPU as general purpose processing element and an ASIC as a custom designed microchip designed for a special application or purpose. Once created, ASICs are non-programmable – they do something very specific (and hopefully very well and very quickly/efficiently). A CPU can run your bitcoin mining program overnight, wake you to Spotify in the morning, let you use your favorite word processor in between games of Plants vs. Zombies, and still let you watch Hulu before you head off to bed.

An ASIP (Application Specific Instruction-Set Processor) bridges the gap between a general purpose processor (CPU) and the highly specific, targeted design of an ASIC. An ASIP will have a much reduced instruction set and a more targeted design towards a specific application (say, digital signal processing), but still allow the execution of a specific instruction set given to it.

Q: Can you mention tools to identify the bottlenecks?

A: Ken: We are trying very hard, particularly in the webcasts themselves, to stay vendor neutral. I don’t mind violating that though here in the Q&A a little bit.

From an open source standpoint, there are a number of tools. One of the more popular now is to use something like Graphana as a front-end to Graphite, and use that to monitor a set of open source (or privately designed) sensors, including sensors from OPM below, that you place throughout your environment.

Here are a few other open-source benchmarking and performance tools, and what aspect of performance to which they apply. Please note that this is not a comprehensive list, nor is this a recommendation for their use. We are providing the link as a convenience, not an endorsement. [http://www.opensourcetesting.org/performance.php]

Still free, but NetApp-centric, is OnCommand Performance Manager (OPM), specifically OPM v2.0 and later. In addition to providing performance metrics for your NetApp storage array, OPM offers up the concept of a “bully” and “victim” scenario – it specifically watches for components that are performing poorly (the “victims”) and helps identify which other components are causing that poor behavior (the “bullies”). My team helps develop OPM.

Not free, and not NetApp centric, but a NetApp product, is OnCommand Insight (OCI). This is a premier product for looking at the performance of the components across your datacenter.

A: Mark: I didn’t want to break the vouch to neutrality. :) EMC has a number of tools as well, vRealize suite, ViPR SRM, Unisphere, plus platform specific tools… However, it has been my experience that the most important tool a performance expert has is still the critical mind. One observes the problem, and then walks the entire set of the SUT layers looking for incongruences. Too often, the perceived bottleneck is not the problem, but a manifestation of a problem somewhere else. For example, as we pointed in the “MiB/s section” of this webcast, the network layer was a bottleneck due to the badly configured OS multipath drivers. Deciphering cause from reason requires several things: a good understanding of the SUT and its layers; a critical mind to analyze problem conditions; and a large dose of curiosity. The latter one a personal trait that drives us to question “what if I change this to that?” Asking questions while troubleshooting is, IMHO, a cornerstone requirement and inherently, a very human trait. My personal view is that tools are just tools, and they require a human hand to operate and a human mind to analyze the results.

Q: Did All flash arrays almost eliminate bottleneck..,at least the Storage controller bottleneck can be eliminated if enterprise can afford all flash arrays?

A: Ken: Actually, almost exactly the opposite. Spinning drives are (now, at least) relatively slow. Over the past 10 years the drives have gotten much bigger, although HDD drive speeds haven’t really changed all that much,. Because of this, what I’ve observed is that the IOPS/GB ratio for HDD has, if anything, been getting worse* and the most common bottleneck for an HDD-based customer turns out to be the speed of their drives.

Now consider what happens when a customer moves to SSDs. The SSDs that are sold (and folks can afford) are generally much smaller than the HDDs they are used to, so customers buy as many of them as they can in order to meet their capacity requirements. And the SSDs are, one-for-one, much faster. So what happens? High drive counts + really fast drives = the drives aren’t your bottleneck anymore. Instead, the bottleneck shifts upstream … in a well architected solution, generally to the storage controller or clients.

*For those that know the terms, we could have a long discussion about working set sizes over the years, how fast data ages, tiered storage and such, and the effect that these have on observed iops/GB … but I think we could agree that since HDD speeds aren’t increasing, the iops/GB ratio isn’t generally getting better.

Q: Can I download this slides?

A: Ken: Absolutely. Here are the links to Part 1 of our series:

PPT and PDF: http://www.snia.org/forums/esf/knowledge/webcasts (look for “Storage Performance Benchmarking: Introduction and Fundamentals (July 2015)”)

Presentation Recording: https://www.brighttalk.com/webcast/663/164323

Q&A Blog: http://sniaesfblog.org/?p=447

Here are the links to Part 2:

PPT and PDF: http://www.snia.org/forums/esf/knowledge/webcasts (look for “Storage Performance Benchmarking: Part 2 (October 2015)”)

Presentation Recording: https://www.brighttalk.com/webcast/663/164335

Q&A Blog: That’s what you’re reading now. :)

Q: Storage controller, is a compute node, right? And for hyper converged systems, storage controller and compute nodes are the same, right?

A: Mark: Most certainly, a Storage Controller can be a compute node, but in our webcast it is not. The term “compute node” is typically interpreted to be a part of the client/hosts layer. A compute node computes for the application, and such application is generating the workload (please see the question above about where workload is initiated).

A good example of the compute node would be a system that renders cartoons, or geodesic fields. As such compute node computes something (application does the work), and stores the results onto the storage controller.

However, in the case of hyper-converged infrastructure, the storage controller is often virtualized among the client hosts, making every compute node a part of a larger storage controller.

Q: Are the performance numbers that vendors publish typically front-end?

A: Mark: I don’t want to generalize published numbers as being one way or another. I recommend reading every publication for specific details. Vendors publish numbers to cover use cases, and each use case may come with its own set of expected measurement points and metrics. Ken and I talked about how metrics matter in the first Storage Performance Benchmarking webcast. :)

Q: “We did an R&D PoC using 32 flash 400GB elements attached on DIMM slots (not through SAS controller, not a direct PCIe attach) and seven 40Gbps cards. We were able to pump 5.5M 4KB-IOPS resulting in 30GB/s (240Gbps) of traffic on the front-end connect. When do you expect the front-end connect be the bottleneck for more standard environment?”

A: Ken: Woot! That sounds like a lot of fun. If you’re in the Raleigh, NC area and can talk about that not under NDA, we should have lunch. I’d like to hear more.

I have a suspicion that this answer won’t satisfy you, because it isn’t going to be as empirical as your example. The problem in answering with raw numbers is that there isn’t a standard configuration for a SUT. An enterprise class storage array with a mix of 40GbE and 32GB FC connections (with traffic over both) will look very different than someone using their old Windows XP box with a single 100Mbit to share out an SMB share, and both will look different than someone accessing their photos on their favorite cloud provider. So, I’ll answer the question by saying that I expect the front-end connect to be the bottleneck anytime the rest of the components in the SUT are capable of hitting your performance metrics (whether that be in terms of response time, IOPS, or data rates), and the front-end connect isn’t.

THAT said, you’d be astounded how often, even today, that MTU mismatches result in terrible front-end performance (and functionality).

Q: “Example of cache in front end connection?”

A: Ken: I’ll cheat and note that SUTs can be a lot more complicated than we showed. For example, our picture looked like this:

 

Benchmarking Image 1

Consider a SUT then where you have:

Benchmarking Image 2

At one level, “the internet” is just a big black box acting as our front-end connect. But if we zoom in on it, perhaps we find that somewhere along the line there’s a caching server. Then we have an easy answer to where you find cache in the front-end connect.

In the much simpler model that you’ll find in many enterprise data environments though, you’ll find that the front-end connect consists of some relatively short length cables and a set of switches – either SAN or NAS switches. And in those environments, you won’t find a lot of cache. You will find memory, but you’ll find it used for buffering more than for caching.

We tried to minimize this in the presentation since there’s not a universally agreed upon distinction between these two terms. I think of a buffer (in this context) primarily as memory set aside to hold data very briefly, after which it is consumed and removed from the buffer. I think of cache, on the other hand, as a storage medium that holds data specifically to speed up data access (storage or retrieval). Data held in a cache can be held for a very long time, and not all data in a cache may ever be consumed/used.

Q: Even SSDs suck at random write but they are good for random read, is there that much difference?

A: Ken: Yes. The data we pulled for drive speeds was real data. And keep in mind that “sucks” is pretty relative here. Enterprise SSDs still tend to be at least 4x faster than spinning media. And, very importantly, their performance is much more consistent and deterministic since seek time is irrelevant with an SSD. New NVRAM technologies, like 3D XPoint, promise to dramatically improve write performance.

DRAM is volatile though so replacing HDDs with that wouldn’t really work, right? But if capacity requirements are high, we cannot replace disks with the cache, right?

A: Mark: Cache should never replace capacity. Cache is temporary storage, and requires by design to move its data to a permanent storage location. The size of cache should be matched to the size of the data that application uses, so called “working area”. For example, if an application writes to a 4GB file (think VMware vmdk), then for best performance the entire 4GB should fit into cache. However, capacity requirements for a VMware datastore can be as high as several TB. If the application (ESX server) is running many VMs, perhaps only the performance few need to fit into cache, while all other VMs would use cache for sub-portions of their vmdks.

A: Ken: You’re right, not permanently. As Mark points out, it isn’t to permanently replace the slower storage with cache necessarily, just supplement it enough that the working set fits in.

Q: How can we make client do less IO? Will it make sense?

A: Mark: A client does less IO by using larger IO size, for example. A classic use case is read- and write-sizes within NFS protocol. It is possible to increase read- and write-size of the NFS protocol from the NFS client mount options side. By default, some Linux environments use 32KB for reads and writes. And reading a 1GB file takes 32768 32KB IOs. If the read size is increased to 1GB, then it takes only 1024 IOs – a 32x reduction!

A: Ken: Other options involve app re-writes (yes, sometimes these ARE possible) and OS upgrades. Perhaps in the “app-rewrite” category, or maybe a new category, I’ve also worked with developers to rewrite their DB queries to be much less disk intensive, for example.

Q: Can you elaborate on some of the client level cache types other than file system or OS?

A: Mark: Other than file system and OS? Hmm… Let’s see: PCI-based cards that cache block-device level cache, e.g. EMC VFCache, SanDisk Fusion-IO, NetApp Flash Cache. Native network protocols (CIFS and NFS) caches. Local database caching, e.g., SafePeak, TimesTen, Windows Azure Caching.

Q: Please add more sessions, which goes into every detail

A: Mark: Absolutely! We will! Promise! We’re shooting for Part 3 in Q1 2016.

Q&A – The Impact of International Data Protection Laws on the Cloud

Alex McDonald

The impact of international data protection legislation on the cloud is complicated and constantly changing. In our recent SNIA Cloud Storage Webcast on this topic we did our best to cover some of the recent global data privacy and data protection regulations being enacted. If you missed the Webcast, I encourage you to watch it on-demand at your convenience. We answered questions during the live event, but as promised we’re providing more complete answers in this blog. If you have additional questions, please comment here and we’ll reply as soon as we can.

The law is complex, and neither SNIA, the authors nor the presenters of this presentation are lawyers. Nothing here or in the presentation should be construed as legal advice. For that you need the services of a qualified professional.

Q. What are your thoughts on Safe Harbour being considered invalid, and the potential for a Safe Harbour 2

A. Since 6 October 2015 when the European Court of Justice invalidated the European Commission’s Safe Harbour Decision, there’s been a lot written about Safe Harbour 2 in the press. But it was clear that a renegotiation was essential two years before that, when discussions for a replacement were started. Many think (and many hope!) that a new and valid agreement in terms of Europe’s Human Rights legislation will be settled between the US and Europe sometime in March 2016.

Q. Are EU Model Clauses still available to use instead of BCRs (Binding Corporate Rules)?

A. EU-US data transfers facilitated by the use of model clauses probably today fail to comply with EU law. But as there appears to be no substitute available, the advice appears to be – use them for now until the problem is fixed. Full guidance can be found on the EC website.

Q. What does imbalance mean relative to consent?

A. An example might help. You might be an employee and agree (the “consent”) to your data being used by your employer in ways that you might not have agreed to normally – perhaps because you feel you can’t refuse because you might lose your job or a promotion for example. That’s an imbalanced relationship, and the consent needs to be seen in that light, and the employer needs to demonstrate that there has been, and will be, no coercion to give consent.

Upcoming December 11 Webcast: Flash Memory Enables 4K and Beyond Video Workflows

Marty Foltyn

by Marty Foltyn

The Consumer Electronics Show (CES), held each year in early January in Las Vegas, has moved a long way from the days when you had to search high and low on the show floor for storage-related exhibits. Step on the floor in 2016, and you may never get past the automobile displays which have the capability to track and store your every activity. And even if you do, the plethora of accessible tech, video imaging, and smart home apps will make your head spin!

Solid State Storage is an important contributor to the internet of things featured at CES, and understanding it is key to making informed choices. Get ready for CES 2016 by first attending a SNIA Solid State Storage webcast on Friday, December 11 at 11:00 am Pacific where Tom Coughlin, CEO of analyst firm Coughlin Associates, presents Flash Memory Enables 4K and Beyond Video Workflows.

As the price and availability of flash memory grows flash memory will enable future generations of media that is even more immersive than today as video moves to 8K and virtual reality begins to play an increasing role in entertainment. Tom will discuss how, as the resolution and frame rate for video increase, flash memory is staring to play a significant role for content capture, post production and content delivery. His presentation will include material from the 2015 Digital Storage in Media and Entertainment Report from Coughlin Associates (and the associated 2015 digital media professional survey) on the growing use of flash memory in all aspects of professional media and entertainment and put flash use in context with other storage technologies in this industry.

The webcast is an important lead in to the CES partner program Storage Visions Conference January 3-4 in Las Vegas, where SNIA will exhibit  solid state and persistent memory and have a pre-conference education day.  Register for this informative SNIA Brighttalk webcast , held on December 11, 2015 at 11:00 apm Pacific/2:00 pm Eastern at https://www.brighttalk.com/webcast/663/180197

Under the Hood with NVMe over Fabrics

J Metz

Non-Volatile Memory Express (NVMe) has piqued the interest of many people in the storage world. Using a robust, efficient, and highly flexible transportation protocol for SSDs, Flash, and future Non-Volatile Memory storage devices, the NVM Express group is working on extending these advantages over a networked Fabric.

Our first Webcast on The Performance Impact of NVMe over Fabrics was very well received. If you missed it, check-it out on-demand. On December 15th, Dave Minturn, Storage Architect at Intel, will join me for a deeper dive in a live Webcast, “Under the Hood with NVMe over Fabrics.” At this Webcast we’ll explain not only what NVMe over Fabrics is, but also specifically pay attention to how it works. We’ll be exploring:

  • Key terms and concepts
  • Differences between NVMe-based fabrics and SCSI-based fabrics
  • Practical examples of NVMe over Fabrics solutions
  • Important future considerations

Register now and join us as we discuss the next iteration of NVMe. I hope to “see” you on the 15th when Dave and I will be anxious to answer your questions.

Life of a Storage Packet (Walk): Q&A

J Metz

We got a lot of great questions at our recent Ethernet Storage Forum webcast “The Life of a Storage Packet (Walk).” As promised, we’ve compiled all the questions with fairly detailed answers. We hope this blog helps to clear up any confusion or uncertainties. If you think of additional questions, please comment below and we’ll get back to you as soon as we can. Thanks to everyone who watched the live webcast. If you missed it, it’s now available on-demand.

Q. Does size of a block depend on OS?

A. Yes, some OS’ only support 512 byte blocks. Some OS’ provide a method to support both 512 byte blocks and 4096 (aka 4K) byte blocks; for example, via a qualifier in their format command. Some devices are built using 4K block sizes, but then emulate 512 byte blocks to the host (aka 512E devices). Many modern versions of OS’ automatically detect the block size of each device they discover and do the right thing based on what they discover. You have to check the documentation for your OS to know its capabilities.

Q. CIFS is not a file system.

A. Not in the same way that ext, ntfs, FAT, HFS, UFS, etc. are, no. However, in terms of certain functionalities that we discussed on the presentation – that is, the ability to manipulate files with operations such as read, write, create, delete, and rename – are all file system functionalities. The difference being, of course, that the files are not on the local computer and are actually on a remote computer.

For what it’s worth, the term ‘CIFS’ has been deprecated from usage, and SMB is the preferred term for precisely the reasons that it should not be confused with local OS systems like the ones mentioned above.

Q. Is it safe to say that a “block” at the file system level is equal to an IO?

A. Not specifically. The difference in the use of those terms, is that a “block” is a place that data is stored – it has an address and it contains data (512 byte of data or 4K bytes of data). An IO is an operation that requests access to a block. An IO may perform a read operation on a block, or it may perform a write operation on a block.

Remember, the term IOPS is I/O operations per second – so it is not about blocks or bytes or bits – it is operations. If the operations are performed on a 512 byte block, they produce a different number of MB/sec than if they operate on a 4K byte block.

So, let’s take an example. A 1MB/second bandwidth on a 4K block size device is the same speed as 1MB/second bandwidth on a 512 byte block size device (observe, however, that the 4K block size device will have only 1/8 the IOPS that the 512 byte device has – because it will take only 1/8 the operations to transfer the same number of Mega-bytes). However, 1M IOPS on a 4K block size device is much better than 1M IOPS on a 512 byte block size device (because the 4K block size device is moving 8X the amount of data than the 512 byte block size device in each operation.

There is an excellent explanation and walk-through of IOPS in our Storage Performance Benchmarking webinar.

Q. Don’t all those Inodes also live on the disk and so don’t the IOs to read those blocks also have to go to the SCSI controller?

A. Well-spotted!

The communication back and forth between the file system and the Inodes traverses the controller for all access to blocks on disk. This is one of the reasons why needing to access disk is considered “expensive.” When you add in a network to the mix, these kinds of situations need particular careful consideration.

Q. Shall we allocate blocks and inodes or is it an automatic process?

A. It’s an automated process, and there is no user intervention at all.

Q. Are Inodes created during OS installation?

A. Inodes are a particular block type, among some other block types (e.g., data blocks, boot blocks, superblocks, group descriptor blocks). These block types are combined into functional groups. These groups are OS-dependent. The block layout therefore, including Inodes, is created during OS installation. If the filesystem needs more Inodes after the OS installation, the OS dynamically adds them to the Inode pool.

Q. Which physical hardware does volume manager reside?

A. Volume managers are not hardware. They are software layers that create pseudo devices that are presented to layers of the OS above them (typically to the file system layer). The volume manager software fits into the OS to accept requests from the file system and pass those requests down to the device driver. In some systems they might be called “filter drivers”.

Q. In flash media, is there also an iSCSI controller that converts PCIe into iSCSI to interact with the flash?

A. I want to make sure that the answer to the question is clear.

On the host, we need to convert PCIe commands to SCSI, so we send them to an iSCSI controller/adapter to be sent across the Ethernet wire. . That adapter can be either software or hardware.

Flash drives are basic media, just like spinning disk drives. Flash will have its own controller, which can be SCSI. If you wish to access the drive over Ethernet using the iSCSI protocol, you will have an adapter on the flash drive (which can be either software or hardware) that will do the SCSI translation between the Flash media and the SCSI commands. This is often called the FTL – or the flash translation layer. Again, the SCSI commands are translated into an Ethernet-friendly packet to be sent along the wire.

There are other types of communication forms for working with Flash, too. The most recent is NVMe. You can see the SNIA webinar on The Performance Impact of NVMe and NVMe over Fabrics for more information.

Q. Why is there a SCSI language in between Storage and the hosts?

A. Before storage standards (like SCSI and ATA), you would purchase storage from Vendor X, and you would also buy a storage controller for that vendor X storage.  If you wanted Vendor Y storage, you could not use the vendor X controller, you had to purchase a new controller from vendor Y. Every vendor had their own language, and you had to purchase matching components.  Once you got locked into one vendor, you were stuck – at the hardware level.

Today with standards (such as SCSI), you can buy a SCSI device from any vendor and connect it to any storage controller that you buy from any vendor – and it just works.  That is the point of the SCSI standard. When the storage standardization efforts began, there were many competing ideas. It just so happened that SCSI won out, and so now it’s everywhere.

Q. If the storage side is flash, do we still need a SCSI controller between host and flash storage or is the controller different for a flash storage?

Yes… and no.

Yes, to use the SCSI part of the OS, the flash device must continue to speak the SCSI protocol and so a SCSI controller is needed. This method of communicating with flash devices enables all the existing S/W on the host OS to just continue working without even knowing it is flash.

No, flash memory chips can be connected to the system using non-SCSI methods. Most of those methods are generally special purpose applications and so the existing OS S/W simply cannot use that device (only the special purpose S/W designed for that device can use it). However, NVMe is a new protocol that is enabling more general use of the flash memory technology with the hopes to provide new capabilities that are beyond what SCSI provides. This is also discussed in our webcast on The Performance Impact of NVMe and NVMe over Fabrics.

Q. What’s the difference between partition, logical disk, volume, LUN, etc?

Excellent question!

Let’s work this one backwards – LUN – that is a SCSI term (actually an acronym) that refers to the Logical Unit Number – it is part of the address used to access a logical unit. Small SCSI devices (such as a single spindle disk drive) have only a single logical unit. Large storage arrays may contain 100s of logical units. Each of those logical units appears to the host OS as if it were a single spindle disk. So, the logical unit is the SCSI object that contains the blocks where the data is stored (where that object may be an individual piece of hardware, or a logical entity within a larger SCSI device). To access a SCSI logical unit, the OS must specify the address of the SCSI device, and then the LUN (logical unit number) for the logical unit within that SCSI device.

The other terms (partition, logical disk, and volume) are OS terms that have to do with virtualization and how the storage blocks are managed. When a SCSI (or other storage device) is formatted by the OS, it may be broken into multiple partitions. Each partition is then treated by the OS as if it were a unique device (a virtual device, or a logical disk). Each of those partitions may then be used independently.

For example, on a Unix system, the “a” partition may contain a file system that has all the files that are necessary to boot. The “b” partition may be setup without a file system and used as the swap or paging storage for use by the virtual memory subsystem. The “d” partition may then contain a file system that contains all the user’s data files. Each partition is unique storage space and may even use a different file system to organize the data located there.

Notice, that I skipped the “c” partition. That partition is often setup to access all the blocks of the physical device. So, on a 500GB disk, maybe “a” contains 10GB, “b” contains 90GB, and “d” contains 400GB; while “c” contains all 500GB. Partitions “a” and “d” may be backed up or restored independently, and partition “c” may be used to perform an image copy of the entire device.

Now, to the other terms:

Logical disk and volume are terms often related to volume managers.

  • Logical disk may be a term used to refer to a partition, but usually that is not the case. Logical disks are typically the devices created by the volume management layer when they combine individual devices into a single larger device (a.k.a. a logical disk).
  • Volume managers also may be used to divide up a large device into small chunks (just like partitions), and those smaller chunks are referred to as logical disks.
  • Volume is a more vague term that typically is used as another term for a logical disk. In some circles, the term Volume is used to refer to a RAID set in a SCSI storage controller (but this is a much less often used definition for Volume).

Q. Will the “complete” presentation somewhere we can go review?

Yes. Click here to access the on-demand webcast as well as a PDF of the webcast slides

Come See SNIA at the Software-Defined Infrastructure Summit

Alex McDonald

Demand for software-defined infrastructure (SDI) is on the rise, and with good reason. SDI helps data centers meet the challenges of cloud computing, big data/analytics, mobility and social media, in an agile and cost-effective way.  I’m pleased to announce that SNIA will be an active participant at next week’s Software-Defined Infrastructure Summit in Santa Clara, CA, December 1-3.

My colleagues and I at the SNIA Cloud Storage Initiative have organized a “Working with OpenStack” Seminar that kicks off the Summit on Tuesday, December 1.

I will keynote an OpenStack fireside chat along with Chris DePuy, VP, at Dell’Oro Group. We’ll be discussing the SNIA Cloud Data Management Interface (CDMI) and its interface with OpenStack, OpenStack implementations, how standards play, and the future of open source in the 21st century.

My keynote will be accompanied by additional SNIA talks in the Introduction to OpenStack session and the Application Management session:

  • Sam Fineberg, PhD, SNIA Cloud Storage Initiative member and Distinguished Technologist at Hewlett Packard Enterprise Storage, will provide an overview of the storage aspects of OpenStack including the core projects for block storage (Cinder) and object storage (Swift), and the new shared file service (Manila). He’ll cover some common configurations and use cases for these technologies, and discuss how they interact with the other parts of OpenStack.
  • Richelle Ahlvers, SNIA Open Source Task Force member and Principal Storage Management Architect at Avago Technologies, will discuss application integration in OpenStack and how SNIA-developed standards enable cross-vendor management interoperability and help open source projects interoperate with more industry solutions.

Tuesday’s Seminar day will include additional sessions from leaders in OpenStack, Ceph, and Software Defined Storage. SDI Summit days 2 and 3 will provide information on hardware, software, and data center technology and applications of software-defined infrastructure featuring keynotes from IBM, Intel, Red Hat, and VMware, all SNIA member companies.  It’s a must attend event.

SNIA will also be exhibiting at the Summit. Please stop by booth #408 to learn how SNIA standards are used in open source projects including cloud data management, non-volatile memory, self-contained information retention, and storage management. We will also have information on SNIA programs such as membership, certification, conformance testing, and conferences.

SNIA members and colleagues can use the code SPGP to receive a $100 discount on any level of SDI Summit registration. I hope to see you in Santa Clara!

Upcoming Webcast: The Impact of International Data Protection Legislation on the Cloud

Alex McDonald

Data Privacy vs. data protection has become a heated debate in businesses around the world as governments across the globe are proposing and enacting strong data privacy and data protection regulations. Join us on November 18th for our next Cloud Storage live Webcast “Data Privacy vs. Data Protection: The Impact of International Data Protection Legislation on the Cloud.”

Mandating frameworks that include noteworthy changes like defining a data breach to include data destruction, adding the right to be forgotten, mandating the practice of breach notifications, and many other new elements are literally changing the rules when it comes to data protection. The implications of this, and other proposed legislation, on how the cloud can be utilized for storing data are significant. Join this live Webcast to hear:

  • “Directives” vs. “regulation”
  • General data protection regulation summary
  • How personal data has been redefined
  • Substantial financial penalties for non-compliance
  • Impact on data protection in the cloud
  • How to prepare now for impending changes

Our experts, Bob Plumridge, SNIA Europe Board Member; Eric Hibbard, Chair SNIA Security TWG, and I will all be available to answer your questions during the event. I encourage you to register today for this timely discussion. We hope to see you on November 18th!

New Webcast: The Life of a Storage Packet (Walk)

J Metz

Wonder how storage really works? When we talk about “Storage” in the context of data centers, it can mean different things to different people. Someone who is developing applications will have a very different perspective than someone who is responsible for managing that data on some form of media. Moreover, someone who is responsible for transporting data from one place to another has their own view that is related to, and yet different from, the previous two.

Add in virtualization and layers of abstraction, from file systems to storage protocols, and things can get very confusing very quickly. Pretty soon people don’t even know the right questions to ask! That’s why we’re hosting our next SNIA Ethernet Storage Webcast, “Life of a Storage Packet (Walk).”

Join us on November 19th to learn how applications and workloads get information. Find out what happens when you need more of it, or faster access to it, or move it far away. This Webcast will take a step back and look at “storage” with a “big picture” perspective, looking at the whole piece and attempting to fill in some of the blanks for you. We’ll be talking about:

  • Applications and RAM
  • Servers and Disks
  • Networks and Storage Types
  • Storage and Distances
  • Tools of the Trade/Offs

The goal of the Webcast is not to make specific recommendations, but equip you with information that will help you ask the relevant questions, as well as get a keener insight to the consequences of storage choices. As always, this event is live, so please bring your questions, we’ll answer as many as we can on the spot. I encourage you to register today. Hope to see you on November 19th!

Assessing SSD Performance in the Data Center

Marty Foltyn

By Marty Foltyn

As solid state drives (SSDs) are deployed in datacenters around the world in both hybrid HDD/SSD and all flash arrays (AFAs), it is becoming increasingly important to understand what metrics are relevant to assess SSD datacenter performance. While the traditional metrics of IO operations per second (IOPS), Bandwidth, and Response Times are commonly used, it is becoming more important to report and understand the ‘Quality of Service’ of those metrics.

eden articleEden Kim, Chair of the SNIA Solid State Storage Technical Working Group, has recently authored an article on Understanding Data Center Workloads. In it, he defines workloads and specifically data center workloads, describes how they are tested, and shows how to measure workloads for performance analysis. Industry standard test methodologies that ensure fair and accurate testing of SSDs both at the device and system level are described, along with how to use them on a reference test platform, Eden also describes in depth Response Time Confidence levels and how an understanding of Demand Variation and Demand Intensity can help the IT administrator assess how a given SSD or array will perform relative to the requirements of an application workload or relative to a specific Response Time Ceiling thus helping in the overall system optimization, design, and deployment.

Read Eden’s full article on the SNIA Solid State Storage Education page at http://www.snia.org/forums/sssi/knowledge/educationBy. Scroll down to “Performance” to find this and a whole range of white papers, tech notes, webcasts, and presentations on this important Solid State Storage topic.

New White Paper: An Updated Overview of NFSv4

AlexMcDonald

Maybe you’ve asked yourself recently; “Hmm, I wonder what’s new in NFSv4?” Maybe (and more likely) you haven’t; but you should.

During the last few years, NFSv4 has become the version of choice for many users, and there are lots of great reasons for making the transition from NFSv3 to NFSv4. Not the least of which is that it’s a relatively straightforward transition.

But there’s more; NFSv4 offers features unavailable in NFSv3. Parallelization, better security, WAN awareness and many other features make it suitable as a file protocol for the next generation of applications. As a proof point, lately we’ve seen new clients of NFSv4 servers beyond the standard Linux client, including support in VMware’s vSphere for virtual machine datastores accessible via NFSv4.

In this updated white paper, An Updated Overview of NFSv4, we explain how NFSv4 is better suited to a wide range of datacenter and high performance compute (HPC) uses than its predecessor NFSv3, as well as providing resources for migrating from v3 to v4.

You’ll learn:

  • How NFSv4 overcomes statelessness issues associated with NFSv3
  • Advantages and features of NFSv4.1 & NFSv4.2
  • What parallel NFS (pNFS) and layouts do
  • How NFSv4 supports performant WAN access

We believe this document makes the argument that users should, at the very least, be evaluating and deploying NFSv4 for use in new projects; and ideally, should be using it wholesale in their existing environments. The information in this white paper is meant to be comprehensive and educational and we hope you find it helpful.

If you have questions or comments after reading this white paper, please comment on this blog and we’ll get back to you as soon as possible.