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

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  • cjb110 - Friday, May 10, 2013 - link

    Pricing will pay a big part I think. As if WD can keep the black SSHD to a small premium then why wouldn't you get it? A proper SSD for main OS, but a 1Tb SSHD for games? Would be interesting to see how that compares to Intel's caching solution? I'd imaging a standalone SSD cache + normal HD is more expensive than a SSHD though.
  • WeaselITB - Friday, May 10, 2013 - link

    This is the sort of comparison that I'd be interested in. If we're looking at desktop or desktop-like parts, then the comparison shouldn't be "SSD + HDD vs SSHD" it should be "SSD + HDD vs SSD + SSHD" -- espeically if the price gap on WD Black HDD to SSHD isn't that great.

  • Kristian Vättö - Friday, May 10, 2013 - link

    The WD Black SSHD will be 2.5" only from what I've heard.
  • kwrzesien - Friday, May 10, 2013 - link

    Kristian: This wasn't clear to me until I got to your comment. Perhaps the last line of the first paragraph could read: "The new 2.5" WD Black that was first showcased at IDF last year"

    +1 for SSD + SSHD. No longer would I have to pick 1-2 games to move to the SSD, they would all be fine on the SSHD and automatically cached depending on which I play the most.
  • Kristian Vättö - Saturday, May 11, 2013 - link

    Edited it so it's clearer now. I guess I was expecting that the OEM-only and custom connector factors would hint towards it being 2.5".
  • philipma1957 - Sunday, May 12, 2013 - link

    As a user of some large apple fusion setups. 1.96tb with the large crucial m5 ssd and 1.5tb with a samsung 830 512gb ssd.

    I can see a future in a 3.5 inch ssd/hdd combo. how about a 3tb western digital red combined with a 256gb ssd.

    IF reliable quite a good drive for boot/gamer pc or for any all in one desk top. The apple fusion tech has proven to run very well for myself and a few heavy user that I built fusion drives for. Would be nice to have a hard wired 1 piece unit in a thunderbolt case. Size and speed that could be moved from pc to pc.
  • Hrel - Monday, May 13, 2013 - link

    Pretty glad to see this, wish it had happened 2 years ago though. Yes, it is faster to have an SSD and hdd, but in laptops that's just not possible most of the time. Certainly not in anything that's actually portable. So if 240GB isn't enough for you then you either choose a hybrid or a hdd. Then there's the obvious expense of buying a 200 dollar SSD and a 100 dollar hdd just to store stuff. I think hybrid drives suit the market and the highest number of end users a lot better than pure SSD's. They're fast, but they're just too expensive. Even in the corporate environment I work in where employees are just now getting 240GB SSD's, they're already complaining about having to carry external hdd's with them everywhere since that's not nearly enough space.

    With that said what I'd really like to see is all laptops ship with (at a minimum) an open mSATA slot. Then you could at least use a 64GB/128GB mSATA SSD and a normal hdd; for those who are willing to spend that much money. Having options is never a bad thing.

    Assuming that happens, what I'd REALLY like to see next is hybrid style caching using said mSATA SSD supported on every laptop motherboard; so you can choose between pure SSD and SSD caching. Since money is the ultimate limiting factor (especially in a corporate environment) it should be expected that they aren't going to budget for a reasonably large SSD (128GB at a minimum) AND a reasonably large HDD (500GB at a minimum).
  • dcollins - Tuesday, May 14, 2013 - link

    I hope this partnership eventually produces a higher end SSHD. I would be willing to plunk down a substantial chunk of cash for a 128GB + 2TB drive as an upgrade for my laptop. I love the speed of an SSD, but I hate having to even think about storage space. That would be the best of both worlds.
  • bsd228 - Thursday, May 16, 2013 - link

    sshd = secure shell daemon.
  • BoloMKXXVIII - Tuesday, May 21, 2013 - link

    Sandisk is probably not the best partner for WD. Sandisk really doesn't need WD as much as WD needs Sandisk.

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