Taking One other Shot at QLC With Cache Tiering

Though Intel is now not straight within the SSD market nowadays, their SSD group and associated applied sciences proceed to stay on below the SK hynix umbrella as Solidigm. Since their preliminary formation on the very finish of 2021, Solidigm has been within the technique of reestablishing their footing, persevering with to promote and help Intel’s earlier SSD portfolio whereas persevering with growth of their subsequent era of SSDs. On the enterprise aspect of issues this lately culminated within the launch of their new D7 SSDs. In the meantime on the patron aspect 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 stage, 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 outstanding. QLC makes for affordable excessive(ish) capability SSDs, which OEMs love, whereas computing fanatics are decidedly much less obsessed with 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 shopper 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 gadgets in an economical method. And whereas Intel’s particular options by no means actually caught on, Intel’s core perception that some type of caching is critical proved right, as all trendy TLC and QLC SSDs include pseudo-SLC caches for improved burst write efficiency.

Whereas they’re divorced from Intel nowadays, 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 blended 3D XPoint/QLC drives such because the Optane Memory 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 position 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 discuss concerning 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 funds QLC drives, it is 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 huge 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 affords 4 lanes of PCIe 4.0, and helps the NVMe 1.4 normal.

As this drive is basically the successor to the Intel 670p, right 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 funds 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 aspect 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 shopper drives in a kind issue smaller than the same old 80mm lengthy M.2 2280 kind issue. Consequently, the corporate may also be producing 2242 kind issue drives in all three capacities, whereas the smallest 2230 kind issue drive will probably be accessible in 512GB and 1TB capacities. These smaller drives are solely meant for the OEM market, nevertheless, so whereas the 2280 drive will probably be bought each at retail and to OEMs, solely the latter will have the ability to formally get their fingers on the shorter drive.

Since Solidigm remains to be utilizing the identical 144L era NAND for this newer product, the write endurance rankings are basically 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 larger than the previous 670p, primarily because of the controller adjustments. Even with a pSLC cache, the QLC NAND is barely 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 vital enchancment in random IOPS (no less than so far as official rankings go).

Lastly, it’s price noting that the “P41” identify will not be a coincidence, even though 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 gained’t all the time 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 go together with SK hynix’s personal Platinum P41 – or because it’s extra generally identified, simply the P41. To make certain, the drives have completely nothing in widespread – the whole lot from the NAND to the controller to the market section is totally different – however SK hynix is ready to supply them collectively, in the event that they resolve to go that route. Sadly, it is 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. Usually, suffixes are used to indicate superior {hardware}, so it’s a really uncommon day when it’s the opposite manner round.

Soldigm Synergy: Learn Caching on Home windows

The {hardware} apart, the opposite main facet of the P41 Plus – and definitely probably the most novel – is Soldigm’s newest try at cache tiering. Whereas the corporate will not be the primary vendor to strive utilizing a pSLC write cache as a learn cache as properly (the Enmotus FuzeDrive takes these honors), that is the primary time Solidigm has gone this route. And it’s actually the best profile try on the method 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 gradual NAND. Whereas going with progressively finer multi-level cells inside NAND causes write efficiency to drop off far quicker than learn efficiency, there may be nonetheless a success. That is particularly the case with regards to 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 shopper workloads to a T.

Solidigm’s answer, 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 somewhat 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 exhibits up as a single SSD. And somewhat than speaking to 2 SSDs, Solidigm merely wants to offer 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 dangerous information is that particular software program/drivers are nonetheless required to determine 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 containers and different machines, to profit in any respect from Solidigm’s learn caching, it must be operating 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 gives drive well being monitoring and different SSD toolbox options. The corporate additionally refers to their total cache tiering characteristic as Synergy, so the characteristic and the software program parts shouldn’t be confused.

The upshot there may be that Solidigm has vital expertise with caching (and caching drivers) at this level. So the corporate ought to have the ability to leverage the expertise and code it already has from earlier merchandise to develop their caching storage driver, versus needing to provide you with the whole lot 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 all the time accessible 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 scale 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 cheap guesses.

As for the effectiveness of Solidigm’s learn caching, based mostly on what we’ve seen with the Optane Reminiscence H20 and related drives, there’s little purpose to doubt that this works, no less than to an extent. Whereas detailed opinions will probably be wanted to kind out the total 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 definitely recognized. The catch will probably be that QLC in pSLC mode will not be 3D XPoint, so whereas it’s quicker than QLC, it gained’t have the ability to supply the identical type of absurd random learn efficiency as Intel’s soon-to-be-retired section change reminiscence.

Solidigm’s personal promotional materials exhibits 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 incredible, 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 properly within the very cache-friendly PCMark 10 Full System Drive take a look at. Solidigm additionally contains an unnamed TLC drive, however with out extra info it’s onerous to say something of worth – and even affirm if it was a significant take a look at.

A win for Solidigm, in any case, doesn’t imply delivering chart-topping efficiency. If the P41 can disguise the dearth of DRAM and nonetheless having the ability to beat different QLC/TLC drives which can be competing within the worth section 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 should always count on to see the brand new QLC drive household earlier than later. The large query, as is often 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 answer, 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.