4 ms·

I didn't have any background on this and didn't know what SMR was. Apparently the background is: people try to add these things to RAID arrays, and when they d

I didn't have any background on this and didn't know what SMR was. Apparently the background is: people try to add these things to RAID arrays, and when they do some rebalancing, the RAID software rejects the disk. The reason is because they use "SMR", which severely hurts random-write performance. The controversy is that it's pretty shady to sell a drive as a "NAS Drive" when the drive is too slow to be usable with any RAID software. (I will spare you my rant on how bad RAID software is. But this is yet another interesting edge case that RAID software doesn't handle and reacts by just blowing away your data.)

Majromax 7y ago
> The reason is because they use "SMR", which severely hurts random-write performance. It hurts random-write performance after a threshold, when an on-disk staging area becomes exhausted. For short bursts, the drive behaves well -- it probably would legitimately work in a RAID array if the array were initialized from a clean slate and not rebuilt. > But this is yet another interesting edge case that RAID software doesn't handle and reacts by just blowing away your data. It's not obvious how a RAID controller should "handle" this. The drives have no outward indication that they suffer from random write saturation. From the controller's perspective, the degraded performance looks very much like a drive failure.
- throwaway2048 7y ago
  A raid array that cant rebuild is near 100% worthless (outside of raid 0)
  - kstrauser 7y ago
    But if the reason it can't rebuild is that the drives are unfit for purpose, you can't really blame the controller.
    - Wowfunhappy 7y ago
      Which is why the manufacturer shouldn't have branded them as NAS drives!
      - kstrauser 7y ago
        You're preaching to the choir. SMR drives are absolutely not NAS-ready, and it's insulting for WD to pretend otherwise.
        magicalhippo 7y ago
        > SMR drives are absolutely not NAS-ready DM-SMR at the very least. If the RAID controller (hardware or software) is SMR-capable, then host-managed or host-aware can work. For example, ZFS with the recent support for separate metadata devices[1] seems to be close to what you'd need for it to become SMR-capable. [1]: https://github.com/openzfs/zfs/pull/5182 https://github.com/openzfs/zfs/pull/5182
        kstrauser 7y ago
        Fair distinction.
- myself248 7y ago
  > the degraded performance looks very much like a drive failure. Sure, but given the choice between "During a rebuild, it looks like another drive isn't doing so well, so I should give up and trash the array" and "During a rebuild, it looks like another drive isn't doing so well, so I should notify the administrator and meanwhile try to maintain as much redundancy as I can" which is the sensible choice?
  - imtringued 7y ago
    There is no choice to be made. Once too many disks fail the entire array has to be taken offline and that's exactly what happens.
    - labawi 7y ago
      Disks "failing" is the problem. If you treat drive state as binary (flawless / eject), you can easily eject too many drives for errors on different 0.000001% of data, crashing the array along with the data.
fmajid 7y ago
In this case there also seems to be a bug in the WD firmware that causes rebuilds to fail, not just be excruciatingly slow.
Tijdreiziger 7y ago
> I will spare you my rant on how bad RAID software is. I am interested in your rant.
toast0 7y ago
RAID software has one thing going for it; at least it's not RAID hardware :P

Majromax 7y ago

> The reason is because they use "SMR", which severely hurts random-write performance. It hurts random-write performance after a threshold, when an on-disk staging area becomes exhausted. For short bursts, the drive behaves well -- it probably would legitimately work in a RAID array if the array were initialized from a clean slate and not rebuilt. > But this is yet another interesting edge case that RAID software doesn't handle and reacts by just blowing away your data. It's not obvious how a RAID controller should "handle" this. The drives have no outward indication that they suffer from random write saturation. From the controller's perspective, the degraded performance looks very much like a drive failure.

throwaway2048 7y ago
A raid array that cant rebuild is near 100% worthless (outside of raid 0)
- kstrauser 7y ago
  But if the reason it can't rebuild is that the drives are unfit for purpose, you can't really blame the controller.
  - Wowfunhappy 7y ago
    Which is why the manufacturer shouldn't have branded them as NAS drives!
    - kstrauser 7y ago
      You're preaching to the choir. SMR drives are absolutely not NAS-ready, and it's insulting for WD to pretend otherwise.
      - magicalhippo 7y ago
        > SMR drives are absolutely not NAS-ready DM-SMR at the very least. If the RAID controller (hardware or software) is SMR-capable, then host-managed or host-aware can work. For example, ZFS with the recent support for separate metadata devices[1] seems to be close to what you'd need for it to become SMR-capable. [1]: https://github.com/openzfs/zfs/pull/5182 https://github.com/openzfs/zfs/pull/5182
        kstrauser 7y ago
        Fair distinction.
myself248 7y ago
> the degraded performance looks very much like a drive failure. Sure, but given the choice between "During a rebuild, it looks like another drive isn't doing so well, so I should give up and trash the array" and "During a rebuild, it looks like another drive isn't doing so well, so I should notify the administrator and meanwhile try to maintain as much redundancy as I can" which is the sensible choice?
- imtringued 7y ago
  There is no choice to be made. Once too many disks fail the entire array has to be taken offline and that's exactly what happens.
  - labawi 7y ago
    Disks "failing" is the problem. If you treat drive state as binary (flawless / eject), you can easily eject too many drives for errors on different 0.000001% of data, crashing the array along with the data.

fmajid 7y ago

In this case there also seems to be a bug in the WD firmware that causes rebuilds to fail, not just be excruciatingly slow.

Tijdreiziger 7y ago

> I will spare you my rant on how bad RAID software is. I am interested in your rant.

toast0 7y ago

RAID software has one thing going for it; at least it's not RAID hardware :P