Yesterday Western Digital and SanDisk announced their collaboration for hybrid hard drives (or SSHDs as they are now called). The idea behind the move is that SanDisk will supply Western Digital with iSSDs (I’ll explain what these are in a bit), which WD will then integrate with their hard drives to act as a read/write cache. The new 2.5" WD Black that was first showcased at IDF last year will be the first fruit of the collaboration, and it will also be WD’s first SSHD.

WD’s approach with SSHDs is slightly different from Seagate’s. Seagate simply put a NAND package on the PCB and used their own controller manage it. SanDisk’s iSSD, on the other hand, is a standalone SSD with a SATA 6Gbps interface in BGA-156 form factor (sometimes called µSSD). Both implementations obviously have their pros and cons: Seagate has total control over the NAND (garbage collection, etc.) but it also means the NAND performance is up to Seagate’s engineers, whereas WD can rely on SanDisk’s expertise on the NAND frontier and concentrate on caching and hard drive technologies.

Now, before we get too excited, putting an iSSD inside a hard drive won’t magically solve the biggest problems that SSHDs have. The first generation WD Black will only have 8GB-32GB of NAND, which is better (or the same) than Seagate’s SSHD (or Momentus XT as it was called previously) but it’s still not enough to provide performance that is even close to the SSD-only experience. SanDisk promises pretty impressive numbers for the iSSD (450/350MBps sequential read/write, 9K/1K IOPS random read/write), but those are for the largest 128GB SKU. Remember that one of the key elements of SSD performance is high parallelism: The more NAND you have, the better the performance is because you can access multiple dies simultaneously. As the Black SSHD will only have up to 32GB of NAND, it won’t be able to achieve a similar level of performance as the 4x larger 128GB model.

With increasing NAND densities the performance difference between capacities has become an even bigger issue because performance decreases with every process node, yet capacity per die goes up. This is a double-whammy that results in lower parallelism (and hence performance) at the smallest capacities. With SLC NAND you could somewhat dodge the performance issue since SLC NAND is faster to begin with, but unfortunately the iSSD is MLC based (which shouldn’t surprise anyone given the pricing of SLC NAND).

When you combine the very limited amount of NAND with a low-power integrated controller, it’s simply impossible to get performance that’s anywhere close to a decent standalone SSD. Of course there’s the caching side too because only a small portion of your data can be stored in the NAND, so in most cases you will still be limited by the spinning platters. With 32GB it should finally be possible to cache Windows in full, although the hurdle of hardware-level caching is that you have no say in what goes where.

What’s really special about this announcement is the timing as Seagate introduced their first consumer SSDs only a day earlier. I have a feeling that WD and SanDisk had not planned to go public with their partnership yet but Seagate’s announcement changed their plans. With WD’s biggest rival entering the SSD market, it’s clear that shareholders want to know WD’s strategy in order to maintain credit on the company.

Aside from keeping investors happy, there are also concrete reasons for the partnership. By far the most important one is the fact that SanDisk is a fab owner (a joint-operation with Toshiba where SanDisk gets 49% of the NAND output). Nowadays if you want to do something that requires NAND, there’s no other way to guarantee a steady NAND supply than to partner up with a NAND fabricator. There have already been several NAND shortages in the market (and it's only going to get tougher this year) and the brutal fact is that the ones without a fab or partnership are the last ones in the supply chain.

I’ve already heard from several fab-less SSD OEMs that they have not been able to keep up with demand because there’s not enough NAND in the market. For someone like WD a steady NAND supply is even more important because at least in the beginning the WD Black SSHD is aimed towards OEMs (there's a custom connector so it doesn’t work in regular systems without an adapter). If your production is dependent on the fluctuations of the NAND market, OEMs will likely not choose your product because they don’t want to take the risk of halting their own production due to the lack of drives. It’s not a coincidence that for example Apple sources their SSDs from Samsung, Toshiba, and SanDisk, which are all NAND fabricators.

If WD ever decides to re-enter the SSD market, the partnership will obviously be even more important. I wouldn’t be surprised if WD and SanDisk were actually working on an SSD together. SanDisk has controller IP thanks to the acquisition of Pliant in 2011, but that arm of SanDisk has mainly been focused on the enterprise segment. The consumer market has much lower profits and it’s usually not profitable to design a consumer-grade controller on your own, but with a partner like WD it can turn out to be a good investment as R&D costs can be shared and WD has an enormous distribution channel for providing the product to the market.

All in all, I have a feeling that the real fruits of this partnership won’t be seen today or tomorrow. The WD Black SSHD is definitely an interesting product and we will try to get one in for reviewing as soon as possible, but it's likely that you will still be better off with a small-ish SSD accompanied by a hard drive for storage. My gut is saying that this is more of a transitory product as WD gets ready to re-enter the SSD market. That doesn’t mean it’s the end of story for SSHDs, but this announcement should have happened two, preferably three, years ago.

Source: SanDisk Press Release

Comments Locked


View All Comments

  • jjj - Thursday, May 9, 2013 - link

    You are way way off in thinking Sandisk would make a SSD with WD. Sandisk is pushing hard in SSD and their revenue is quite significant,they hired some new execs too in the last year and at least one of their consumer SSD is quite interesting (you guys should do a review maybe). Sandisk is also a strong consumer brand and with a very wide distribution channel ,they absolutely don't need any help from WD .They are also shipping SSDs to most major notebook OEMs already.They are strong is SAS but not limiting themselvs to just that. They should have PCI drives this year too.
    If anything maybe WD should try to buy Sandisk and become the king of storage. Would not be easy since both companies have about the same market cap so it would be quite a bold move.
    The HDD market might get in real trouble towards the end of the decade. 3D NAND is about to hit the market and there is a chance that in a few gens it could pretty much oust HDDs from the notebook market. 2D NAND can;'t do that but 3D just might. It seems that Samsung will start some kind of production in 2014 while Micron and Sandisk are likely starting in 2015-2016.After than a bit of time will be needed before 3D NAND gets into SSDs, They'll first use it in simpler devices like thumb drives and SD cards and the tech will need some time to mature before maybe prices will be low enough to offer enough storage for most in laptops.And then there is 3D ReRAM, hopefully arriving this decade but it seems too early to understand the impact it will have.
  • Wall Street - Thursday, May 9, 2013 - link

    You are way off...

    They announced the partnership in a press release, this wasn't speculation.
  • jjj - Thursday, May 9, 2013 - link

    How about you pay attention, i was talking about the author speculating that Sandisk and WD would make a SSD together.
  • Gigaplex - Thursday, May 9, 2013 - link

    That partnership is for the SSHD, not a standalone SSD, as Sandisk is quite capable of doing that on their own.
  • designerfx - Sunday, May 12, 2013 - link

    yep, as in the only part that isn't in that high demand.

    Cache may be able to make up for a large part of access delay, but once a drive spins up it's still so much slower than an SSD that the only reason I want for physical disks is for the cheap WD reds. Anything else I can't see why anyone would want to suggest a hybrid when they keep making the same obvious mistake: trying to peg it as more performance focused and intentionally keeping the platters really small.

    If SSHD was 4TB *today*? then we'd be onto something.

    a SSHD, even if it's significantly faster than the last generation, is simply a lower quality/poorer performing SSD.
  • BernardV - Friday, May 10, 2013 - link

    Really dislike Sandisk products. WD should really not be involved with them beyond this project. I also think you work for Sandisk ;)
  • jabber - Sunday, May 12, 2013 - link

    I have bought several Sandisk SSD's of different marks and they have all been excellent in performance and value. In fact they are my go to SSD make for general use.

    However, I have a few of their standard USB sticks and they are woeful! Oh 2MBps transfer speed...fantastic!
  • Kristian Vättö - Friday, May 10, 2013 - link

    We have reviewed the Ultra Plus, if that's what you meant (the Extreme is SandForce based so this is the only one that I would count as interesting):

    SanDisk is big in the enterprise side (they already have PCIe SSDs too, check out the Lightning) but I find that their consumer products are a bit "meh". The Extreme is just another SandForce based drive. The Ultra Plus is decent but its performance is lacking compared to other offerings on the market (it's not slow by any means but marketing is all about big numbers). The U100 (sold as "SanDisk SSD") is just horrible and I don't understand why it even exists anymore.

    The problem is, WD needs something of its own if they want their second try in the SSD market to be longer than the first. It's too late for WD to jump on the SandForce bandwagon because they don't have any advantage compared to every other fab-less SandForce OEM. SanDisk can survive in the market without WD, that's for sure, but they likely don't want to invest on a consumer-grade controller on their own since you need a high volume to make the investment profitable (and hence there's high risk involved). There is much less risk involved if you team up and share the R&D costs. Sure, you will lose exclusivity, but volumes will be higher and that results in lower unit production costs.

    My point is, WD needs a partner for their SSDs. Out of the NAND fabricators, SanDisk is definitely the best fit as they also have controller IP but their consumer products could use an uplift. This could just be a meaningless press release which basically says "hey we are buying iSSDs from SanDisk" but I'm pretty confident that there is more to this partnership. But this is speculation of course; there is no right and wrong (yet), only different views.

    As for 3D NAND, we don't know enough about it to really speculate its impact. The R&D costs behind it are enormous and it will also require different manufacturing equipment, so it won't be cheap at first. If analysts are to believe, hard drive shipments will remain rather steady and the market isn't dying:
  • futrtrubl - Friday, May 10, 2013 - link

    I have to disagree about one thing here. You talk about higher volumes, but they are already working at capacity. Increase volumes, aka demand since supply is already maxed, in the consumer market brings nothing for them when they can use all of their capacity on higher margin enterprise parts. I think most SDD manufacturers would ditch the consumer market completely if it wasn't that it's a good place to dump parts that don't make the grade and that they are trying to keep mindshare for when capacity again exceeds enterprise demand.
  • Wall Street - Thursday, May 9, 2013 - link

    I think the article writer should try a 32 GB cache drive before he writes it off. I'm using a Sandisk ReadyCache and the speedup is phenomenal. I was fooling around with the partitions and the cache reset and the slowdown was immediately noticeable. I think that 32 GB seems to be enough to speed up Windows, Photoshop, Chrome, Office and 1-2 games. I am guessing it is one of those 90/10 rules where 10% of the data is accessed 90% of the time.

    I know that the lack of dies also limits performance, but going from no SSD to SSD seems to get 90% of the boost that is achieveable. Even really fast SSDs only shave a few more seconds off Windows boot time, it isn't like doubling SSD speeds can halve boot times again like going from HDD to SSD can.

Log in

Don't have an account? Sign up now