Taking Another Shot at QLC With Cache Tiering

Though Intel is now not straight within the SSD market today, their SSD staff and associated applied sciences proceed to reside on underneath the SK hynix umbrella as Solidigm. Since their preliminary formation on the very finish of 2021, Solidigm has been within the strategy of reestablishing their footing, persevering with to promote and help Intel’s earlier SSD portfolio whereas persevering with improvement of their subsequent era of SSDs. On the enterprise facet of issues this not too long ago culminated within the launch of their new D7 SSDs. In the meantime on the patron facet of issues, right now at Flash Reminiscence Summit the corporate is saying their first post-Intel client SSD, the Solidigm P41 Plus

The P41 Plus is, at a excessive degree, the successor to Intel’s 670p SSD, the corporate’s second-generation QLC-based SSD. And based mostly on that description alone, a 3rd era QLC drive from Soldigm is one thing that few AnandTech readers would discover exceptional. QLC makes for reasonable excessive(ish) capability SSDs, which OEMs love, whereas computing fanatics are decidedly much less smitten by them.

However then the P41 Plus isn’t only a conventional QLC drive.

One of many extra attention-grabbing ventures out of Intel’s time as a consumer SSD producer was the corporate’s forays into cache tiering. Whether or not it was utilizing flash reminiscence as a tough drive cache, utilizing 3D XPoint as a tough drive cache, and even utilizing 3D XPoint as a flash reminiscence cache, Intel tried a number of methods to hurry up the efficiency of slower storage units in a cheap method. And whereas Intel’s particular options by no means actually caught on, Intel’s core perception that some form of caching is important proved appropriate, as all trendy TLC and QLC SSDs include pseudo-SLC caches for improved burst write efficiency.

Whereas they’re divorced from Intel today, Solidigm is choosing up proper the place Intel left off, persevering with to experiment with cache tiering. Coming from the identical group that developed Intel’s combined 3D XPoint/QLC drives such because the Optane Reminiscence H20, Solidigm now not has entry to Intel’s 3D XPoint reminiscence (and shortly, neither will Intel). However they do have entry to flash reminiscence. So for his or her first solo client drive as a stand-alone subsidiary, Solidigm is taking a recent stab at cache tiering, increasing the function of the pSLC cache to function each a write cache and a learn cache.

P41 Plus {Hardware}: The “Plus” Stands For Worth

However earlier than we dive an excessive amount of into Solidigm’s newest caching configuration, let’s speak in regards to the {hardware} itself.

The Solidigm P41 Plus, codenamed Echo Harbor, is a PCIe 4.0 x4 QLC SSD that’s based mostly round what’s now Solidigm’s 144L QLC NAND. More and more typical for finances QLC drives, this can be a DRAMless design, so it depends om Host Reminiscence Buffer (HMB) to retailer the interpretation tables.

Driving the brand new SSD is Silicon Movement’s SM2269XT controller. Launched a bit earlier this yr, the SM2269XT is by and enormous an up to date model of the SM2267XT, and serves as the corporate’s mainstream 4-channel DRAMless controller. Constructed on a 12nm course of, the SM2269XT helps NAND switch charges as much as 1600 MT/s, and is designed to be paired with both TLC or QLC NAND. In the meantime for host connectivity, the 2269XT gives 4 lanes of PCIe 4.0, and helps the NVMe 1.4 normal.

As this drive is basically the successor to the Intel 670p, all the way down to utilizing the identical 144L NAND, it finally ends up coming in the identical three capacities: 2TB, 1TB, and 512GB. Relative to the 670p, Solidigm has turned up the pSLC cache sizes a bit; the drives supply a most of 75GB, 150GB, and 300GB of SLC cache respectively, which diminishes because the drive fills.

As a result of it lacks any DRAM, the P41 Plus is much more of a finances drive than its predecessors. Whereas the 660p and 670p include DRAM, the P41 Plus is the primary Intel/Solidigm pure QLC drive to forego the DRAM. Solidigm is up-front that they’re going after the worth market with this drive, and eradicating the DRAM from a QLC drive is unambiguously a price play.

One of many facet advantages of eradicating the DRAM, nevertheless, is that it reduces the quantity of house taken up by the drive. Consequently, for the primary time Solidigm is ready to supply one in every of their consumer drives in a type issue smaller than the same old 80mm lengthy M.2 2280 type issue. Consequently, the corporate may also be producing 2242 type issue drives in all three capacities, whereas the smallest 2230 type issue drive will likely be obtainable in 512GB and 1TB capacities. These smaller drives are solely meant for the OEM market, nevertheless, so whereas the 2280 drive will likely be bought each at retail and to OEMs, solely the latter will be capable of formally get their palms on the shorter drive.

Since Solidigm remains to be utilizing the identical 144L era NAND for this newer product, the write endurance scores are primarily unchanged from their earlier era merchandise. Which means a 200 TBW ranking for the 512GB drive, after which 400 TBW and 800 TBW respectively for the 1TB and 2TB drives. Unfold out over the 5 yr guarantee interval for the drive, and this works out to about 0.2 drive writes per day, or an endurance ranking of 400 P/E cycles.

General, the rated efficiency of the P41 Plus is greater than the previous 670p, primarily because of the controller adjustments. Even with a pSLC cache, the QLC NAND is simply barely quick sufficient to warrant PCIe 4.0 connectivity, although the sequential reads can hit 4125MB/sec. This makes for modest will increase in sequential throughput, whereas providing a extra important enchancment in random IOPS (not less than so far as official scores go).

Lastly, it’s price noting that the “P41” identify shouldn’t be a coincidence, even if it’s already in use elsewhere. Whereas Solidigm is a subsidiary of SK hynix, it’s a part of the mega reminiscence agency all the identical. And whereas SK hynix’s personal inner retail efforts are separate from Solidigm proper now, that received’t at all times be the case. So, even when slowly, SK hynix is making preparations for a day the place they’ve a single retail model.

The top result’s that the P41 Plus has been named to associate with SK hynix’s personal Platinum P41 – or because it’s extra generally recognized, simply the P41. To make certain, the drives have completely nothing in frequent – every part from the NAND to the controller to the market phase is completely different – however SK hynix is ready to supply them collectively, in the event that they determine to go that route. Sadly, this can be a doubtful determination from a buyer standpoint; whereas the (Platinum) P41 is a flagship-level drive designed for prime efficiency, the P41 Plus is a the very reverse finish of the spectrum – very “plus” certainly. Typically, suffixes are used to indicate superior {hardware}, so it’s a really uncommon day when it’s the opposite means round.

Soldigm Synergy: Learn Caching on Home windows

The {hardware} apart, the opposite main facet of the P41 Plus – and definitely essentially the most novel – is Soldigm’s newest try at cache tiering. Whereas the corporate shouldn’t be the primary vendor to attempt utilizing a pSLC write cache as a learn cache as nicely (the Enmotus FuzeDrive takes these honors), that is the primary time Solidigm has gone this route. And it’s definitely the very best profile try on the approach but.

As with the Optane Reminiscence sequence of drives and the Enmotus drive, the fundamental thought behind having a learn cache is to additional enhance the efficiency of a drive with in any other case sluggish NAND. Whereas going with progressively finer multi-level cells inside NAND causes write efficiency to drop off far sooner than learn efficiency, there’s nonetheless a success. That is particularly the case in terms of random reads in addition to low queue depth operations that may’t absolutely exploit the parallelism current in a SSD. And sadly, that additionally describes consumer workloads to a T.

Solidigm’s resolution, then, is to deal with the pSLC cache not as a write cache that’s merely used to buffer small quantities of information earlier than it may be written to the slower QLC NAND, however relatively to make use of the pSLC cache as a scorching cache for reads and writes. Which means maintaining scorching knowledge (LBAs) on the pSLC cache, and solely sending knowledge to the QLC portion of the NAND when it’s both deemed now not scorching, or when the house is required (e.g. the pSLC portion is being shrunk). This works out to being similar to how the Optane Reminiscence H20 and its ilk operated, simply changing the Optane cache with the pSLC NAND.

The excellent news is that from a technical standpoint, this considerably simplifies the development (and abstraction) of the drive. Whereas the Optane Reminiscence H20 had the unlucky want to indicate up and function as two drives – one Optane, one QLC – the P41 Plus reveals up as a single SSD. And relatively than speaking to 2 SSDs, Solidigm merely wants to supply hints to the drive’s firmware to let it know what knowledge it ought to take into account scorching. This shuffles extra of the workload behind cache tiering on to the drive controller itself.

The unhealthy information is that particular software program/drivers are nonetheless required to establish scorching knowledge and supply instructions to the drive controller. And that software program, in flip, is Home windows-only. So whereas the P41 Plus will work on Linux bins and different machines, to profit in any respect from Solidigm’s learn caching, it must be working on a Home windows host with Solidigm’s driver.

For the launch of the P41 Plus, Soldigm is (re)branding their software program suite as Soldigm Synergy. That is comprised of their storage driver, in addition to a separate storage device that provides drive well being monitoring and different SSD toolbox options. The corporate additionally refers to their general cache tiering function as Synergy, so the function and the software program parts shouldn’t be confused.

The upshot there’s that Solidigm has important expertise with caching (and caching drivers) at this level. So the corporate ought to be capable of leverage the expertise and code it already has from earlier merchandise to develop their caching storage driver, versus needing to provide you with every part from scratch.

In response to Solidigm, they don’t put aside any house on the P41 Plus particularly to carry scorching knowledge for reads. So the complete capability of the drive is at all times obtainable for entry, with the dimensions of the pSLC cache dynamically altered based mostly on how a lot of the drive’s capability is in use. And whereas we don’t have detailed figures for every capability of the drive, Solidigm has indicated that they solely do learn caching when the drive is lower than half-full. After the drive is half-full, the drive shifts to working like a extra conventional QLC SSD, favoring the diminishing pSLC house for writes to cut back the painful penalty of writing on to QLC. For the 512GB drive, the pSLC cache will go down as little as 8GB if the drive is stuffed, and whereas we don’t have formal figures for the opposite drives, 16GB and 32GB respectively are affordable guesses.

As for the effectiveness of Solidigm’s learn caching, based mostly on what we’ve seen with the Optane Reminiscence H20 and comparable drives, there’s little motive to doubt that this works, not less than to an extent. Whereas detailed opinions will likely be wanted to kind out the complete efficiency vary of the drive, we’ve already seen that throwing a quick cache in entrance of a DRAM-equipped QLC drive can enhance efficiency, particularly in workloads the place the recent knowledge is well recognized. The catch will likely be that QLC in pSLC mode shouldn’t be 3D XPoint, so whereas it’s sooner than QLC, it received’t be capable of supply the identical form of absurd random learn efficiency as Intel’s soon-to-be-retired section change reminiscence.

Solidigm’s personal promotional materials reveals modest enhancements. Combined learn/write (70/30) workloads at QD1 measured with iometer present a 66% enchancment in IOPS, reaching 25K. Pure random reads enhance a bit extra, going up by 72% to round 18K IOPS.

To make certain, neither of those figures is unbelievable, nevertheless for a QLC drive they’re respectable, and above what the extra conventional drives just like the 670p have delivered in our testing.

Solidigm additionally has some barely extra real-world benchmarks, which have the P41 Plus performing nicely within the very cache-friendly PCMark 10 Full System Drive check. Solidigm additionally contains an unnamed TLC drive, however with out extra info it’s arduous to say something of worth – and even affirm if it was a significant check.

A win for Solidigm, in any case, doesn’t imply delivering chart-topping efficiency. If the P41 can cover the shortage of DRAM and nonetheless with the ability to beat different QLC/TLC drives which might be competing within the worth phase alongside the P41 Plus, then that’s a win for Solidigm.

Closing Ideas

Wrapping issues up, whereas Solidigm isn’t saying a launch date for the P41 Plus this morning, based mostly on early retail listings we must always anticipate to see the brand new QLC drive household earlier than later. The large query, as is normally the case with QLC drives, is at what worth. QLC drives are nonetheless at a elementary technical drawback in comparison with TLC drives, so even with the potential advantages of a greater caching resolution, the P41 Plus household nonetheless must be priced competitively. As with Intel and Solidigm’s earlier QLC drives, pricing goes to make or break issues within the retail market.