Category: NFS

Introducing the Networking Storage Forum

John Kim

At SNIA, we are dedicated to staying on top of storage trends and technologies to fulfill our mission as a globally recognized and trusted authority for storage leadership, standards, and technology expertise. For the last several years, the Ethernet Storage Forum has been working hard to provide high quality educational and informational material related to all kinds of storage.

From our “Everything You Wanted To Know About Storage But Were Too Proud To Ask” series, to the absolutely phenomenal (and required viewing) “Storage Performance Benchmarking” series to the “Great Storage Debates” series, we’ve produced dozens of hours of material.

Technologies have evolved and we’ve come to a point where there’s a need to understand how these systems and architectures work – beyond just the type of wire that is used. Today, there are new systems that are bringing storage to completely new audiences. From scale-up to scale-out, from disaggregated to hyperconverged, RDMA, and NVMe-oF – there is more to storage networking than just your favorite transport. Read More

Common Questions on Clustered File Systems

John Kim

More than 350 people have already seen our SNIA Ethernet Storage Forum (ESF) webcast “Clustered File Systems: No Limits.” Our presenters, James Coomer and Jerry Lotto, did a great job explaining what clustered file systems are, key considerations, choices and performance. As we expected, there were plenty of questions, so as promised, here are answers to them all.

Q: Parallel NFS (pNFS) has been in development/standard effort for a long time, and I believe pNFS is not in the Linux kernel it appears pNFS is yet to be prime time.

A: pNFS has been in Linux for over a decade! Clients and server are widely available, and you should look at the SNIA White Paper “An Updated Overview of NFSv4; NFSv4.0, NFSv4.1, pNFS, and NFSv4.2” for more information on the current state of play.

Q: Why the emphasis on parallel I/O? Any single storage server can feed results at link capacity, so you do not need multiple storage servers to feed a client at full speed. Isn’t the more critical issue the bottleneck on access to metadata for a single directory or file? Federated NAS bottlenecks updates for each directory behind a single master server?

A: Any one storage server can usually saturate one client, but often there are multiple hungry clients making requests simultaneously. Using parallel I/O allows multiple servers to feed multiple high-bandwidth clients across a narrow or wide set of data. This smooths out the I/O load on the servers in a near-perfect manner regardless of the number of clients performing I/O. It is absolutely true that metadata serving can become a bottleneck, so parallel file systems use cached and/or distributed metadata to overcome this and again, every client takes part in that interaction and shares some responsibility for managing communicating metadata updates.

Q: Can any application access parallel file system (i.e. through an agent in the driver level)? Or does it require specific code within the application?

A: Native access to a parallel file system requires a specific client or agent in the host, but many parallel file systems allow any client to access the data through a NAS protocol gateway. No changes are needed to applications to use a parallel file system – These parallel file systems are mounted as a POSIX compliant file system and therefore adhere to basically the same standards as an NFS mount for example.

Q: Are parallel file system clients compatible with scale-out NAS servers?

A: Nearly all scale-out NAS servers speak a standard NAS protocol like NFS or SMB. Clients running a parallel file system client can also access NAS via these standard protocols. Exceptions to this may possibly (but none that we know of) occur for scale-out NAS servers that support a modified NFS/SMB protocol or a custom NAS client which might conceivably conflict with the parallel file system client when installed on an OS.

Q: Of course I am biased, but I am fond of the AFS (Andrew File System) Family of File Systems.   There is OpenAFS, but there is also what we are doing at AuriStor extending beyond the core AFS global namespace model (security functionality, and performance)

A: AFS is another distributed file system which supports large scale deployments, native clients for many platforms, and strong security features. It also uses local caching of files to improve performance. It uses a weakly consistent file locking system so multiple clients can access the same file simultaneously but they cannot both update the same file at the same time. OpenAFS is an open-source implementation of AFS. Auristor (formerly Your File System, Inc.) is a startup providing a commercial parallel file system that is compatible with AFS.

Q: I am more familiar with Veritas Cluster File System, could you please do a quick compare with Lustre or GPFS?

A: The Veritas Cluster File System (formerly VxCFS, now part of Veritas InfoScale) is a distributed file system that runs on Linux and popular flavors of Unix. It supports up to 64 nodes and allows multiple nodes to share the same back-end storage hardware. Comparing it to Lustre and GPFS is beyond the scope of this webinar, but in basic terms, parallel file systems can offer far greater scalability and bandwidth for example, through the use of optimized RDMA clients for high performance networks.

Q: Why do file apps need shared access to data, but block apps do not?

A: Traditionally block storage did not offer shared access to data (except when used as shared back-end storage for a clustered file system), while apps that needed shared access to data usually chose to use a NAS protocol such as SMB or NFS. So in many cases file-based apps use file sharing protocols because they need shared access to data from multiple clients. (In other cases file-based applications do not require sharing but the storage administrators believe it’s easier to manage or less expensive than networked block storage.)

Q: Do Lustre and GPFS have SMB Direct support?

A: Not today. SMB Direct is an option to use RDMA and multi-channel with the SMB 3 protocol. Both Lustre and GPFS support the ability to export a file system via NFS or SMB, but generally they do not support SMB Direct yet. Both Lustre and GPFS support RDMA access through their clients.

How to the clients avoid doing simultaneous writes to the same file?

A: Some parallel file systems allow this by letting different clients write to different parts of the same file. Others do not allow this. In either case, distributed file locking is used to prevent two clients from writing simultaneously to the same part of a file (or to the same file if it’s not allowed).

Q: How can you say that the application “does not have to worry about” how the clustered file system serializes writes? Doesn’t this require continuous end-to-end connectivity?

A: When the application writes data it generally writes to a POSIX-compliant file system and does not need to worry about how the parallel file system serializes, distributes, or protects the data because this is virtualized (managed) by the file system. It usually does require continuous end-to-end connectivity from the clients to the servers, though in some cases caching could allow for brief gaps in connectivity and in some systems not every client needs to have network connectivity to every server. There are multiple mechanisms within parallel file systems to manage the various cases of clients/servers disappearing from the network, temporarily or permanently (whilst for example holding a lock).

Q: How does a parallel file system handle the sequences of write on a same file? Just append one by one? What if a client modified a line?

A: This is the biggest challenge for and reason to use a parallel file system.  Beneath the covers, coherency is maintained by Spectrum Scale using a token management server process which issues locks for object requests.  Similar functionality is implemented in Lustre using a distributed lock manager.  These objects are most commonly blocks within files rather than entire files, but this is application controlled.  The end result is a POSIX-compliant interface that scales to thousands of clients.

Q: What does FPO stand for?

A: File Placement Optimizer – a shared-nothing architecture and licensing model for IBM Spectrum Scale (aka GPFS). Learn more here.

Q: Is there a concept in parallel file systems for “auto-tuning” yet? Seems like the early days of SAN management and tuning…

A: Default tuning values are optimized for general purpose workloads, but the whole purpose of tuning parameters is to adjust away from those defaults to optimize the file system for a particular application workload or fil esystem architecture.  Both IBM and OpenSFS with the support of Intel have published extensive documentation on best practices for optimization and tuning for either file system.  We are not aware of any work on “automating” that process but there has been recent work (e.g. in spectrum scale) to simplify the tuning process.

Q: Which is better as interconnect between disk and servers, shared access or share-nothing?

A: The use of shared access in the interconnect between disks and servers is limited to providing HA functionality in Lustre or Spectrum Scale, the ability to service I/O requests to a storage device if the server which has primary responsibility for that device is not available.  This usually involves multiple server-attached external storage which can add cost to building the file system.  The alternative approach to HA is to replicate blocks of data to different disks on different servers, cutting back on the usable capacity of the file system.  If HA is not a requirement, a share-nothing architecture will generally involve less hardware and therefore be less expensive to build.

If you have more questions, please comment on this blog. And I encourage you to check out the SNIA ESF webcast library for educational, vendor-neutral content on Ethernet networked storage topics

Clustered File Systems: No Limits

John Kim

Today’s storage world would appear to have been divided into three major and mutually exclusive categories: block, file and object storage. The marketing that shapes much of the user demand would appear to suggest that these are three quite distinct animals, and many systems are sold as exclusively either SAN for block, NAS for file or object. And object is often conflated with cloud, a consumption model that can in reality be block, file or object.

A fixed taxonomy that divides the storage world this way is very limiting, and can be confusing; for instance, when we talk about cloud. How should providers and users buy and consume their storage? Are there other classifications that might help in providing storage solutions to meet specific or more general application needs? What about customers who need file access performance beyond what one storage box can provide? Which options support those who want scale-out solution like object storage with file protocol semantics?

To clear up the confusion, the SNIA Ethernet Storage Forum is hosting a live Webcast, “Clustered File Systems: No Limits.” In this Webcast we will explore clustered storage solutions that not only provide multiple end users access to shared storage over a network, but allow the storage itself to be distributed and managed over multiple discrete storage systems. You’ll hear:

  • General principles and specific clustered and distributed systems and the facilities they provide built on the underlying storage
  • Better known file systems like NFS, IBM Spectrum Scale (GPFS) and Lustre, along with a few of the less well known
  • How object based systems like S3 have blurred the lines between them and traditional file based solutions

This Webcast should appeal to those interested in exploring some of the different ways of accessing & managing storage, and how that might affect how storage systems are provisioned and consumed. POSIX and other acronyms may be mentioned, but no rocket science beyond a general understanding of the principles of storage will be assumed. Contains no nuts and is suitable for vegans!

As always, our experts will be on hand to answer your questions on the spot. Register now for this October 25th event.

 

NFS FAQ – Test Your Knowledge

Chad Hintz

How would you rate your NFS knowledge? That’s the question Alex McDonald and I asked our audience at our recent live Webcast, “What is NFS?.” From those who considered themselves to be an NFS expert to those who thought NFS was a bit of a mystery, we got some great questions. As promised, here are answers to all of them. If you think of additional questions, please comment in this blog and we’ll get back to you as soon as we can.

Q. I hope you touch on dNFS in your presentation

A. Oracle Direct NFS (dNFS) is a client built into Oracle’s database system that Oracle claims provides faster and more scalable access to NFS servers. As it’s proprietary, SNIA doesn’t really have much to say about it; we’re vendor neutral, and it’s not the only proprietary NFS client out there. But you can read more here if you wish at the Oracle site.

Q. Will you be talking about pNFS?

A. We did a series of NFS presentations that covered pNFS a little while ago. You can find them here.

Q. What is the difference between SMB vs. CIFS? And what is SAMBA? Is it a type of SMB protocol?

A. It’s best explained in this tutorial that covers SMB. Samba is the open source implementation of SMB for Linux. Information on Samba can be found here.

Q. Will you touch upon how file permissions are maintained when users come from an SMB or a non-SMB connection? What are best practices?

A. Although NFS and SMB share some common terminology for security (ACLs or Access Control Lists) the implementations are different. The ACL security model in SMB is richer than the NFS file security model. I touched on some of those differences during the Webcast, but my advice is; don’t expect the two security domains of SMB (or Samba, the open source equivalent) and NFS to perfectly overlap. Where possible, try to avoid the requirement, but if you do need the ability to file share, talk to your NFS server supplier. A Google search on “nfs smb mixed mode” will also bring up tips and best practices.

Q. How do you tune and benchmark NFSv4?

A. That’s a topic in its own right! This paper gives an overview and how-to of benchmarking NFS; but it doesn’t explain what you might do to tune the system. It’s too difficult to give generic advice here, except to say that vendors should be relied on to provide their experience. If it’s a commercial solution, they will have lots of experience based on a wide variety of use cases and workloads.

Q. Is using NFS to provide block storage a common use case?

A. No, it’s still fairly unusual. The most common use case is for files in directories. Object and block support are relatively new, and there are more NFS “personalities” being developed, see our ESF Webcast on NFSv4.2 for more information. 

Q. Can you comment about file locking issues over NFS?

A. Locking is needed by NFS to maintain file consistency in the face of multiple readers and writers. Locking in NVSv3 was difficult to manage; if a server failed or clients went AWOL, then the lock manager would be left with potentially thousands of stale locks. They often required manual purging. NFSv4 simplifies that by being a stateful protocol, and by integrating the lock management functions and employing timeouts and state, it can manage client and server recovery much more gracefully. Locks are, in the main, automatically released or refreshed after a failure.

 Q. Where do things like AFS come into play? Above NFS? Below NFS? Something completely different?

A. AFS is another distributed file system, but it is not POSIX compliant. It influenced but is not directly related to NFS. Its use is relatively small; SMB and NFS dominate. Wikipedia has a good overview.

Q. As you said NFSv4 can hide some of the directories when exporting to clients. Can this operation hide different folders for different clients?

A. Yes. It’s possible to maintain completely different exports to expose or hide whatever directories on the server you wish. The pseudo file system is built separately for each server export. So you can have export X with subdirectories A B and C; or export Y with subdirectories B and C only.

Q. Similar to DFS-N and DFS-R in combination, if a user moves to a different location, does NFS have a similar methodology?

A. I’m not sure what DFS-N and DFS-R do in terms of location transparency. NFS can be set up such that if you can contact a particular server, and if you have the correct permissions, you should be able to see the same exports regardless of where the client is running.

Q. Which daemons should be running on server side and client side for accessing filesystem over NFS?

A. This is NFS server and client specific. You need to look at the documentation that comes with each.

Q. Regarding VMware 6.0. Why use NFS over FC?

A. Good question but you’ll need to speak to VMware to get that question answered. It depends on the application, your infrastructure, your costs, and the workload.

Next Live Webcast: NFS 101

Chad Hintz

Need a primer on NFS? On March 23, 2106, The Ethernet Storage Forum (ESF) will present a live Webcast “What is NFS? An NFS Primer.” The popular and ubiquitous Network File System (NFS) is a standard protocol that allows applications to store and manage data on a remote computer or server. NFS provides two services; a network part that connects users or clients to a remote system or server; and a file-based view of the data. Together these provide a seamless environment that masks the differences between local files and remote files.

At this Webcast, Alex McDonald, SNIA ESF Vice Chair, will provide an introduction and overview presentation to NFS. Geared for technologists and tech managers interested in understanding:

  • NFS history and development
  • The facilities and services NFS provides
  • Why NFS rose in popularity to dominate file based services
  • Why NFS continues to be important in the cloud

As always, the Webcast will be live and Alex and I will be on hand to answer your questions. Register today. Alex and I look forward to hearing from you on March 23rd.

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.

What to Expect from OpenStack Manila Liberty

AlexMcDonald

On October 7, 2015, the SNIA Ethernet Storage Forum is pleased to present its next live Webcast on OpenStack Manila. Manila is the OpenStack file share service that provides the management of file shares (for example, NFS and CIFS) as a core service to OpenStack. Intended to be an open-standards, highly-available and fault-tolerant component of OpenStack, Manila also aims to provide API-compatibility with popular systems like Amazon EC2.

I will be moderating this Webcast, presented by the OpenStack Manila Project Team Lead (PTL), Ben Swartzlander, who will dive into:

  • An overview of Manila
  • New features that are being delivered for OpenStack Liberty (due October 2015)
  • A preview of Makita

With Liberty availability due next month, this information is extremely timely; I encourage you to register now to block your calendar. This will be a live and interactive Webcast, please bring your questions. I look forward to “seeing” you on October 7th.

NFS 4.2 Q&A

AlexMcDonald

We received several great questions at our What’s New in NFS 4.2 Webcast. We did not have time to answer them all, so here is a complete Q&A from the live event. If you missed it, it’s now available on demand.

Q. Are there commercial Linux or windows distributions available which have adopted pNFS?

A. Yes. RedHat RHEL6.2, Suse SLES 11.3 and Ubuntu 14.10 all support the pNFS capable client. There aren’t any pNFS servers on Linux so far; but commercial systems such as NetApp (file pNFS), EMC (block pNFS), Panasas (object pNFS) and maybe others support pNFS servers. Microsoft Windows has no client or server support for pNFS.

Q. Are we able to prevent it from going back to NFS v3 if we want to ensure file lock management?

A. An NFSv4 mount (mount -t nfs4) won’t fall back to an nfs3 mount. See man mount for details.

Q. Can pNFS metadata servers forward clients to other metadata servers?

A. No, not currently.

Q. Can pNfs provide a way similar to synchronous writes? So data’s instantly safe in at least 2 locations?

A. No; that kind of replication is a feature of the data servers. It’s not covered by the NFSv4.1 or pNFS specification.

Q. Does hole punching depend on underlying file system in server?

A. If the underlying server supports it, then hole punching will be supported. The client & server do this silently; a user of the mount isn’t aware that it’s happening.

Q. How are Ethernet Trunks formed? By the OS or by the NFS client or NFS Server or other?

A. Currently, they’re not! Although trunking is specified and is optional, there are no servers that support it.

Q. How do you think vVols could impact NFS and VMware’s use of NFS?

A. VMware has committed to supporting NFSv4.1 and there is currently support in vSphere 6. vVols adds another opportunity for clients to inform the server with IO hints; it is an area of active development.

Q. In pNFS, does the callback call to the client must come from the original-called-to metadata server?

A. Yes, the callback originates from the MDS.

Q. Is hole punched in block units?

A. That depends on the server.

Q. Is there any functionality like SMB continuous availability?

A. Since it’s a function of the server, and much of the server’s capabilities are unspecified in NFSv4, the answer is – it depends. It’s a question for the vendor of your server.

Q. NFS has historically not been used in large HPC cluster environments for cluster-wide storage, for performance reasons. Do you see these changes as potentially improving this situation?

A. Yes. There’s much work being done on the performance side, and the cluster parallelism that pNFS brings will have it outperform NFSv3 once clients employ more of its capabilities.

Q. Speaking of the Amazon adoption for NFSv4.0. Do you have insight / guess on why Amazon did not select NFSv4.1, which has a lot more performance / scalability advantages over NFSv4.0?

A. No, none at all.

Next Webcast: What’s New in NFS 4.2

AlexMcDonald

We’re excited to announce our next ESF Webcast on NFSv4.2. With NFSv4.1 implemented on several commercial NFS systems, an established Linux client and a new pNFS Linux server, there is a continued growth of NFS usage in the IT industry. NFSv4.1, first introduced in 2010, meets many needs in the modern datacenter, but there are still technologies and advanced techniques that NFS developers want to deliver.

Join me and J Metz on April 28th at 10:00 a.m. PT as we’ll cover a brief update of where we are with NFSv4.1 and more detail on the proposed features for NFSv4.2 that are currently being ratified at the IETF. This will be a live, interactive session. Register now and please bring your questions.

If you need a primer on NFS before this event, I encourage you to check our 4-part Webcast mini-series available on demand:

Register today. I hope to see you on April 28th.