What’s the state of SAS? Will the 24G standard help SAS drives thrive in an increasingly NVMe-oriented data center landscape?
Introduced in 2004, SAS drives are known for greater reliability and higher overall data transfer rates compared with their SATA counterparts. From every angle, SAS (Serial Attached SCSI) drives are designed with the data center in mind.
All incumbents face challenges though, and for SAS (and the wider SCSI stack) that challenge comes in the form of flash—specifically flash-native NVMe. As advances in AI drive demand for low-latency storage solutions, the question emerges: can SAS survive for the long term?
SAS, SATA, and NVMe
The Serial Attached SCSI (SAS) and Serial Advanced Technology Attachment (SATA) both debuted in the early 2000s, but targeted different markets. SAS was built for enterprise environments, prioritizing reliability and performance for 24/7 operation in servers and data centers. SATA, meanwhile, focused on consumer devices where cost-effectiveness mattered more than raw speed or uptime.
Nipping at the heels of SAS, however, is NVMe (Non-Volatile Memory Express), which began development in 2007 and became commercially available in 2012. Here, the trend lines are clear. The IDC estimates that 80% of SSDs shipped in 2024 used NVMe, a huge shift from the 36% figure in 2020. According to a report by Market Glass Inc., the NVMe market will continue to grow at a CAGR of 29.5% between 2025 and 2032.
SAS Drives: Timeline and Overview
2004: SAS arrives on the scene as SAS-1 (3.0 Gbit/s).
2007: SAS rival NVMe begins development.
2012: NVMe becomes commercially available.
2017: The SAS-4 specification (commonly called 24G SAS, or 22.5 Gbit/s) arrives.
The state of play is this. Consumer and nearline HDD deployments are predominantly SATA native. SSDs are increasingly moving towards NVMe. This suggests that SAS is in danger of getting squeezed out of the equation. However, as with so much in data centers, whether SAS infrastructure remains an important part of storage architectures comes down to costs.
Nearline HDD Remains Key
HDD has retained its dominant role in storing data cheaply at scale. Across the traditional and cloud data center, the lion’s share of commercially stored exabytes—approximately 80% at last count, to be precise—sits not on flash but on spinning media. And until NVMe-native HDD comes into its own (see below), the most affordable way to closely integrate tiers behind a single interface is to use SAS.
SATA and Backwards Compatibility
The majority (around 67.55%) of the installed base of hard drives are SATA native. However, even SATA native drives generally sit behind SAS infrastructure. SATA and SAS are one-way compatible: You can plug a SATA drive into a SAS controller, but not vice versa.
This has two upshots. Firstly it means, again, that SAS is a workable option for integrating HDDs and SSDs into hybrid architectures. SSDs rarely use SATA anymore: this year, the market share of the flash market held by SATA SSDs will likely dip below 10%. Although SSDs increasingly use NVMe, this interface is not backward compatible with either SAS or SATA.
Mixing and Matching in Turbulent Times
In traditional tiered setups, low-latency operations on hot storage are handled by high-performance SSD, while HDDs remain the best option for storing a massive amount of data at scale at a low $/TB. While AI has done much to make alternative arrangements more attractive, the fact remains that many of these options are unaffordable to smaller players. This is especially true at a time when the AI supercycle has led to a massive storage crunch.
After all, there’s every indication that the volume of exabytes sitting with hyperscalers will continue to rapidly grow in the next few years. Industry analyst Tom Coughlin projects that in 2029, there will be 7.3ZB of shipped HDD capacity.
The upshot is clear: we are in the midst of a huge and sustained explosion in data generation. Here, having HDDs and SSDs alike sit behind behind a backwards-compatible interface like SAS can be an advantage, allowing ITAD procurement teams to mix and match drive types more easily. This all-hands-on-deck situation is good news for SAS.
NVMe For HDD
But before we consider the case closed for the continued relevance of SAS, there is another tantalizing scenario to bear in mind. What if NVMe miraculously extends to hard drives? Seagate has been actively working on such drives. Meanwhile, Western Digital is engaged in a concerted push to expand HDD bandwidth. SATA cannot support this bandwidth, while SAS and NVMe can. But if most flash already uses NVMe, then leaning into NVMe HDD would be a smart move for high-bandwidth drives.
However, NVMe for HDD faces some real challenges. Even the most state-of-the-art HDDs aren’t fast enough to take advantage of the high-speed transfer PCIe allows. And this is unlikely to change soon, as disks usually spin at the standard 7200 rpm.
So, while NVMe for HDD is a powerful concept—think of the massive parallelism NVMe could bring to high capacity, multi-actuator HDDs—it has a number of technical and implementation challenges ahead of it.
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NVMe could do much to simplify hybrid architectures by avoiding the bridges, adapters, and controllers that SAS/SATA-based HDDs need when put in an NVMe-environment.
Given the long-haul challenges SAS faces, it’s little surprise that SCSI advocates focus on improving SAS to keep it competitive.
24G SAS
Here the centerpiece is the development of 24G SAS, a doubling of bandwidth from 12 Gbps. 24G was a long time coming: SCSI Trade Association agreed on the Gen 4 specification way back in 2017.
SAS 24G is backwards compatible to 12G SAS (and 6G SAS / SATA), built for enterprise reliability, and offers “a lot more room for innovation in the SCSI stack,” says Kutcipal. Technologies such as SMR and multi-actuator drives have “come into primetime at 24G.” Compared with the 12G standard, the new specification offers such features as forward error correction and continuous adaptation, STA’s Kutcipal explains.
Despite these products, there are relatively few 24G SAS flash options to choose from. There are also few, if any, 24G SAS disk drives currently on the market. Rather than doubling throughput again to 48Gbps, the next move is 24G+, which offers no speed boost, focusing instead on reliability and ecosystem improvements.
Chris Mellor at Blocks & Files infers that SCSI is effectively “ceding the high-speed drive interface area to NVMe, [while] it sees a continuing role for SAS in hyperscale storage environments”. Since SAS HDD dominates here, it seems that the fortunes of SAS will be tied quite tightly to those of HDD in the coming years.
Value SAS
Another relatively recent development in SAS is the emergence of value SAS (vSAS) for solid state drives. Marketed as a new class of SSDs, vSAS drives offer many of the benefits of SAS while aiming for close to parity pricing with enterprise SATA SSD. (To achieve the lower pricing, the manufacturers removed dual port support and the T10 data integrity field while reducing sector size to a maximum of 512 bytes.)
Driving The Future
While the game is far from up for either SAS or SATA drives, the performance boost of NVMe positions the flash-native protocol favorably for the future, particularly as low-latency AI applications continue to be a central concern in data center design.
The reality remains nuanced, particularly in the cloud environment. “It’s pretty clear that SSD and NVMe-based platforms will continue to grow in the coming years as new hardware deployments better optimized to today’s needs and edge applications displace legacy ones,” says Stephen Buckler, chief operating officer of Horizon Technology.
“At the same time, I wouldn’t bet against HDD—the jury remains out. Remember that NAND fab capacity is costly to build. Ultimately, much will depend on the drive makers’ development of HAMR technology to support their roadmaps toward truly massive-capacity drives.”
If the fate of SAS is indeed tied to that of HDD, the future for SAS appears more promising than the proponents of all-flash, NVMe-based solutions might suggest.
SAS Drives and The Data Tsunami
There’s so much data in the offing— a tidal wave of bits breaking as we speak—that it seems quite likely that data center HDD (buoyed by its favorable economics) will hold its place as the primary storage medium for mass data in the decade ahead.
And within this explosive context, it seems equally likely that SAS will retain its status as a tried and tested interface for affordable mass data storage—at least for the foreseeable future. Nonetheless, we’ll be keeping a close eye on the continued surge in NVMe flash, and the impact this will have on the share of interfaces in the storage mix.
For real-time pricing and market insights on SAS drives, get in touch with the expert team at Horizon Technology. With 25 years’ experience managing enterprise drives and enjoying trusted relationships with each of the major drive makers, we offer solutions that will meet your needs while exceeding your expectations.
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