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Shingled Magnetic Recording drives—unlike this
Los Angeles
-class submarine—aren't on anybody's list of "Fast Attack" vessels.
Michael Meilen / ETC Robert Gulini
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SMR where you least expect it
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Seagate says Network Attached Storage and SMR don’t mix
View more stories
Storage vendors, including but reportedly not limited to Western Digital, have quietly begun shipping SMR (Shingled Magnetic Recording) disks in place of earlier CMR (Conventional Magnetic Recording) disks.
SMR is a technology that allows vendors to eke out higher storage densities, netting more TB capacity on the same number of platters—or fewer platters, for the same amount of TB.
Until recently, the technology has only been seen in very large disks, which were typically clearly marked as "archival". In addition to higher capacities, SMR is associated with much lower random I/O performance than CMR disks offer.
Hey, is that a periscope?
Storage vendors appear to be getting much bolder about deploying the new technology into ever-smaller formats, presumably to save a bit on manufacturing costs. A few weeks ago, a
message
popped up on the zfs-discuss mailing list:
The unexpected shift from CMR to SMR in these NAS (Network Attached Storage) drives has caused problems above and beyond simple performance; the user quoted above couldn't get his SMR disks to stay in his ZFS storage array at all.
There has been speculation that the drives got kicked out of the arrays due to long timeouts—SMR disks need to perform garbage-collection routines in the background and store incoming writes in a small CMR-encoded write-cache area of the disk, before moving them to the main SMR encoded storage.
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It's possible that long periods of time with no new writes accepted triggered failure-detection routines that marked the disk as bad. We don't know the details for certain, but several users have reported that these disks cannot be successfully used in their NAS systems—despite the fact that the name of the actual product is
WD Red NAS Hard Drive
.
Western Digital responds
In the weeks since this issue first began cropping up on mailing lists, Western Digital has responded differently in different venues. The same user who reported difficulties in the zfs-discuss list opened a smartmontools
ticket
and reported an emailed response from Yemi Elegunde, an enterprise and channel sales manager for Western Digital UK:
Further Reading
HAMR don’t hurt ’em—laser-assisted hard drives are coming in 2020
As several users pointed out in the smartmontools thread, it seems likely that Elegunde was conflating SMR and
HAMR
technologies. WD Ultrastar 14TB and 20TB drives have been available since 2018 and have SMR written
right on the label
.
This morning, Elegunde replied with a correction in the form of an official statement from Western Digital. Emphasis below is ours, not Western Digital's:
Separately, another Western Digital spokesperson responded to inquiries from
blocksandfiles.com
:
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Conclusions
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One of these disks is inordinately slower than the other and costs less to manufacture. Can you guess which one?
Jim Salter / camelcamelcamel
The writing on the wall here seems clear. Yes, Western Digital slid SMR drives into traditional, non-enterprise channels—and no, the company doesn't feel bad about it, and you shouldn't expect it to stop.
What really grinds our gears about this is that the only conceivable reason to shift to SMR technology in such small disks—lowered manufacturing costs due to fewer platters required—doesn't seem to be being passed down to the consumer. The screenshot above shows the Amazon price of a WD Red 2TB EFRX and WD Red 2TB EFAX—the EFRX is the faster CMR drive, and the EFAX is the much slower SMR drive.
Western Digital doesn't appear to be the only hard drive manufacturer doing this—blocksandfiles has confirmed quiet, undocumented use of SMR in small retail drives from
Seagate
and
Toshiba
as well.
We suspect the greater ire aimed at Western Digital is due both to the prominent NAS branding of the Red line and the general best-in-class reputation it has enjoyed in that role for several years.
Further Reading
Seagate says Network Attached Storage and SMR don’t mix
Update April 21:
a Seagate representative has
clarified
that while some Barracuda desktop drives are SMR, their entire NAS-oriented Ironwolf and Ironwolf Pro line are CMR only.
