Western Digital Releases First EAMR Disks in 18TB, 20TB Capacities
Earlier this month, WD promised it would release 16TB and 18TB of its EAMR drives, with a 20TB SMR drive to follow. This week, it made good on the first two promises: WD Gold EAMR drives are now available for purchase.
EAMR stands for Energy Assisted Magnetic Recording, and it’s Western Digital’s own technology for increasing hard drives. While WD was originally set to deploy MAMR (Microwave Assisted Magnetic Recording), the company changed directions and opted to deploy a technology it claims is the result of its research into both HAMR and MAMR. Seagate has chosen to deploy HAMR (Heat Assisted Magnetic Recording) and argued that it has superior scalability over the long term, but the difficulty of bringing the feature to market has allowed WD to get EAMR into market before its rival.
EAMR works by applying electricity to the main pole of the write head. This additional energy alters the state of the bits in each track and allows them to be packed more tightly. Importantly, this technique works on both CMR / PMR drives and SMR drives, allowing WD to improve capacity across the board. WD now has a 20TB SMR drive in qualification. Like most high-capacity drives, this is a helium-filled hard drive. Filling the drive with helium instead of normal air allows the drive heads to spin with much faster, with less resistance. Old air-filled hard drives topped out around 5 platters, maybe six at the very most, while these drives pack up to 9.
The reason increasing HDD capacity required developing technologies like EAMR and HAMR in the first place is due to a classic iron triangle of competing problems. First, the magnetic field required to disrupt data on the drive must be stronger than the influence of any single grain on the HDD platter, to prevent drives from literally changing their own data. The smaller and tighter you pack data on the platter, the higher the magnetic coercivity factor has to be.
That causes issues. No matter how high the magnetic coercivity is, the drive write head must be capable of generating an even stronger field in order to properly write data. Finally, the drive write head’s field has to be small, to prevent the disk from overwriting data that it isn’t supposed to be accessing. You can pack more data on a drive by narrowing the magnetic field, but this will weaken the field strength. If the field strength is too weak, the write head will be unable to overcome the magnetic coercivity of the HDD platters.
SMR (shingled magnetic recording) solves this problem by taking advantage of how we can read data in a narrower magnetic field than we can write it. These drives have read speeds close to their standard counterparts, but their write speeds are much lower because the drive must perform a program/erase cycle very similar to what SSDs use in order to write new data to the drive. Drives are divided into zones, with a typical zone size of 256MB. If you change 10KB of a 256MB zone, the drive has to read the contents of the zone, insert the new data, and then overwrite the entire 256MB block.
The SMR drives that we’ve discussed recently have all been drive-managed products, but WD’s upcoming 20TB disk is host-managed and intended for enterprise deployments. All three new drives use a three-stage actuator in an actuator – milliactuator – microactuator configuration. This three-stage actuator system supposedly allowed WD to increase density further.
I’ve always had a sneaky admiration for hard drives. While their performance hasn’t been anything to write home about in at least a decade, and the capacity gap between solid-state and spinning disk storage is shrinking, enterprises will have a home for drives like this for some time to come. If you need a lot of storage and don’t want to spend a lot of money, HDDs still beat SSDs by a significant margin. The 16GB WD Gold is selling for $528, while the 18GB drive is priced at $593. WD has the drives currently for sale in its own store, while Newegg states they’ll be available on 7/24.
Also, as an FYI: Neither WD nor Seagate hit their intended launch targets. The launch below refers to specific years, but neither WD nor Seagate got their enhanced drives out as quickly as they forecast. For a peek at how long Seagate has worked on HAMR, check out this ET story from 2002.