Hard drives, as far as I’m concerned, are now storage pools. They offer more storage capacity than your average SSD and cost quite a bit less when you look at per-gigabyte prices. They’re mostly reliable, so long as they pass the six-month and two-year mark (after six months it’s probably reliable, and after two years it’ll probably go on for four more). Recently a new type of hard drive has become somewhat popular amongst both consumers and businesses, called an SSHD (Solid State Hybrid Drive). That’s exactly what the WD Blue 4TB drive I have on hand is, and it’s a rather interesting product.
For first impressions, the sheer weight of the drive makes it feel expensive, and four terabytes has never felt so heavy. It’s complemented by an MLC-based SSD with 8GB of memory for caching purposes. Most drives ship with caches of between 32MB and 128MB, so this is a vast improvement over previous models. The cache is there to bridge the price and performance gap to a regular SSD and to an extent it does work. SSHDs cache copies of the most-used files on the drive for quicker access, so actions like booting your OS or running a game off this drive might be as fast as most budget SSDs out there.
When copying to the drive, the cache also acts as a buffer. For short periods of sustained writes to the drive you can expect the speeds to ramp up to about 160MB/s, but that’s because all of the data is going to the cache first. After that, speeds drop and the average will depend on what you’re copying. Transferring MP4 videos from my 1.5TB Samsung drive resulted in average speeds of about 55MB/s, while copying my Steam games folder resulted in average write speeds that were around 35MB/s. This is in stark contrast to the synthetic tests I ran in HD Tune and CrystalDisk Mark, which showed that instantaneous read and write speeds almost always hit the cache first.
As fast as this drive appears to be for mass storage, I’d never advocate using it as your main system drive or as your game drive because the caching algorithm is too aggressive. I loaded up Civilization V and Borderlands: The Pre-Sequel, and there was a noticeable delay in swapping from one to the other. After running Borderlands for the first time, subsequent runs saw the levels load quicker, as the files were being read from the cache instead of the drive itself. Swapping games reset and filled the cache, which isn’t very ideal.
With that in mind, where would you use this drive? I can see some synergy with an HTPC, because the only thing you’re loading into the cache is the OS, while the media files won’t. I can also see this being used for a PFSense router, because the cache will be able to load up the saved copies of websites you visit frequently, giving you much lower load times, and you can optionally use the extra space partitioned off into a shared network drive. Outside of those applications though, I can’t recommend the WD Blue 4TB SSHD as your only system drive, because the 8GB cache is just not enough for a desktop use case.