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[Editor’s Note: This is the first in a series of upcoming blog posts discussing 24G SAS features.]

By: Cameron T. Brett (SCSI Trade Association), with contributions from Tim Symons (Microchip) and Alvin Cox (Seagate), October 21, 2019

Serial Attached SCSI (SAS) and the SCSI protocol continue to innovate with one of the storage industry’s longest running technology roadmaps. Today’s 12Gb/s SAS is moving to 24G, and some 24G ecosystem elements are sampling today. SAS became the industry benchmark for high reliability, availability and scalability (RAS) by delivering per lane performance, data integrity, flexible architectures and scalability in enterprise servers and storage for decades. SAS is becoming less expensive to deploy with the highest capacity SSD and HDD storage devices, along with the introduction of Value SAS.

So what’s next for SAS? The SAS-4 specification is in the publication process and products are well into development. 24G SAS brings a significant performance speed bump, nearly doubling the current data rate, but it also brings SSD, QoS, data reliability and signal improvements.

20-bit Forward Error Correction (FEC)
In short, FEC enhances data integrity as electrical signal transmission rates increase (like from 12Gb/s → 22.5Gb/s). Faster data rates increase the probability of bit errors at the physical layer, hence improved error correction is required. Forward error correction enables the signal receiver with the ability to correct errors without re-transmitting the data. Without going too far into the technical weeds, Reed-Solomon codes are used to create parity elements, or “symbols”, that are transmitted with the data. SAS uses a very short (150-bits) code length for low latency. The 20-bits of FEC code can fix up to two errors in each transmission.

A benefit of using FEC is a reduced number of re-transmissions, or retries. Data integrity is improved, and that means SAS can successfully transmit more transactions than other protocols that do not use FEC by reducing the need to retransmit when corrupted data is found.

Where Does FEC Benefit the System?
During transmission of data over a SAS-4 (24G SAS) channel, the signal is impacted by physical impairments, including crosstalk, reflections and poor signal-to-noise ratio, resulting in bit errors at the receiving end of the transmission. If a bit is uncorrectable, even by FEC, it will be transmitted again so the fewer the re-transmissions the better. The FEC implementation in the SAS-4 specification will correct most bit errors, but occasionally one will get through, which translates to one uncorrectable bit error every 12.3 hours. Not too bad, having to do one retransmission only twice a day, compared with multiple re-transmissions if FEC is not available.

Persistent Memory software development has been a source of server development innovation for the last couple years.  The availability of the open source PMDK libraries (http://pmem.io/pmdk/) has provided a common interface for developing across PM types as well as server architectures.  Innovation beyond PMDK also continues to grow, as more experimentation yields open and closed source products and tools. However, there is still hesitation to develop without physical systems.  While systems are available from a variety of outlets, the costs of those systems and the memory can still be a barrier for small developers.  Recognizing that there’s a need to grow both outlet and opportunity, Now, however, the Storage Networking Industry Association (SNIA) is announcing the availability of NVDIMM-based Persistent Memory systems for developers along with a programming challenge. Read More

SNIA technical work and education advances will play a prominent role in the program at the 2019 Flash Memory Summit, August 5-8, 2019, in Santa Clara, CA.  Over 40 speakers will present on key standards activities and education initiatives, including the first ever FMS Persistent Memory Hackathon hosted by SNIA.  Check out your favorite technology (or all), and learn what SNIA is doing in these sessions: SNIA-At-A-Glance

• •SNIA Solid State Storage Reception Monday, August 5, 5:30 pm, Room 209/210
• •SNIA Standards mainstage presentation by Michael Oros, SNIA Executive Director Tuesday, August 6, 2:50 pm, Mission City Ballroom
• •Beer and Pizza with SNIA Experts on Persistent Memory/NVDIMM, Remote Persistent Memory/Open Fabrics, SNIA Swordfish, and more Tuesday, August 6, 7:15 pm – 9:00 pm, Ballrooms A-C
• •SNIA Solid State Storage Initiative booth #820 featuring Persistent Memory demos and Performance, Computational Storage, and SNIA Swordfish discussions Tuesday, August 6, 4:00 pm – 7:00 pm; Wednesday August 7, Noon to 7 pm; and Thursday, August 8, 10:00 am – 2:30 pm, Exhibit Hall

Persistent Memory Read More

UCSD Computer Science and Engineering, the Non-Volatile Systems Laboratory, and the Storage Networking Industry Association (SNIA) are inviting submissions of proposals for presentation at the first annual Persistent Programming in Real Life (PIRL) conference.  PIRL brings together software development leaders interested in learning about programming methodologies for persistent memories and sharing their experiences with others. This is a meeting for developer project leads on the front lines of persistent programming; not sales, marketing, or non-technical management. Read More

A new SNIA specification offers a unified approach to managing storage and servers in environments like hyperscale and cloud infrastructures.  SNIA on Storage recently sat down with SNIA member volunteers from the Scalable Storage Management Technical Work Group (SSM TWG), who just announced the completion of Version 1.0 of the SNIA Swordfish^TM storage management specification, to learn more.

SNIA on Storage (SOS): What prompted SNIA to begin work in this area?

SSM TWG:  We have been looking at what IT administrators are doing in today’s data centers, and what they will need to do in the future with storage equipment and storage services.  We wanted to simplify the way storage is allocated, monitored, and managed, so the SNIA SSM TWG was formed and members collaborated to develop SNIA Swordfish, a specification that extends the DMTF’s (Distributed Management Task Force) Redfish™.  Redfish is an open industry standard specification and schema that specifies a RESTful interface and utilizes JavaScript Object Notation and Open Data Protocol to help customers integrate solutions within their existing tool chains.

SOS:  What does SNIA Swordfish do?

SSM TWG:  Our SNIA Swordfish specification is based on Redfish’s easy-to-use RESTful interface, and provides a scalable storage management application programming interface (API) that can handle all necessary storage management functionality, including file and block storage provisioning, volume mapping and masking, replication, and capacity and health reporting tools.  SNIA Swordfish can assist in handling tasks such as locating storage with a suitable class of service and allocating it to a server or a virtual machine.

SOS:  How will SNIA Swordfish fit into data center management?

SSM TWG:  SNIA Swordfish was designed to support management use cases that focus on what IT administrators need to do with storage equipment and storage services in a data center. Because it extends the DMTF Redfish API into storage management, it  helps provide a unified approach for managing servers, storage, and network fabrics. This unified approach will make it easier to create management software tools that can deal with operations involving multiple management domains. SNIA Swordfish is also designed to support vendor specific functionality alongside standardized functionality, to allow for future needs.

SOS:  Which companies are working on SNIA Swordfish in the TWG?

SSM TWG:  Our TWG members represent many of the leading companies in the storage industry today, including Broadcom, Dell EMC, HPE, Intel, Microsoft, NetApp, Nimble Storage, and VMware.

SOS:  Where can IT administrators and data center managers learn more about SNIA Swordfish?

SNIA Swordfish will be a highlight of the SNIA Storage Developer conference September 19-22 in Santa Clara, CA, with overview and deep dive presentations.  These presentations will be made publicly available on the SDC website at www.storagedeveloper.org.  SNIA Swordfish has its own webpage at www.snia.org/swordfish.   Those who would like to submit feedback on the specification can do so either via the SSM TWG (SNIA members) or the SNIA Feedback Portal (all).