There seems to be no limit to the capacity of "traditional" hard disks: Western Digital has just pushed back one more!
Until a few years ago, it seemed that the limit to the number of platters that could be integrated into a single 3.5" hard disk was 9. Seagate itself seemed hardly confident that it would be possible to go beyond this without increasing the thickness of these hard disks, which are no longer used in private homes, but are used in the very popular and very greedy data centers. The cost per gigabyte of these hard disks is far better than that of SSDs, and for these capacity ogres, this makes all the difference. The good news is that this "9-platter limit" was first broken down to 10 platters, and now Western Digital is even announcing 11 platters in units that are not prototypes, but models already on the market.
The 32 GB Ultrastar DC HC690 in detail © Western Digital
First up is the Ultrastar DC HC590, an 11-platter hard drive based on Energy-assisted PMR or ePMR technology, which achieves a capacity of 26TB thanks to a platter density of 2.36TB. There's also a 24TB version, and in either case, we're talking about a rotational speed of 7,200 rpm for data rates of 302 MB/s. Alongside this model, Western Digital also offers the Ultrastar DC HC690, based on Shingled Magnetic Recording or SMR, which overlays tracks to further increase the density of the platters: a maximum of 2.9 TB per platter. This allows Western Digital to market two models: 30 and 32 TB with a throughput of 260 MB/s at an identical rotation speed of 7,200 rpm.
It's interesting to note Takaaki Deguchi's comments on the official Western Digital blog. The head of design at Western Digital in Fujisawa (Japan) explains the challenge his team faced: " Without changing the overall height [of the hard disk], we asked ourselves how we could add an extra disk. [...] We either had to reduce the spacing between the disks, or the thickness of the disk, or other elements such as the molding of the base or the thickness of the top cover ". A challenge that seems increasingly difficult to meet, even if Western Digital already seems to be planning 40 or even 50 TB ePMR and SMR hard disks. To go beyond this, however, the platters will have to be made denser, and technologies such as HAMR or MAMR will have to be used.
