Adventures in ZFS: Faulted Cache Devices

Adventures in ZFS: Faulted Cache Devices

We recently had an issue with Crucial M4 Solid State Disks when using them with ZFS on Solaris 11 Express (snv_151a).  Basically the disks were showing a whole bunch of write errors and had been “FAULTED” by ZFS. Now to make this problem even worse when we tried to zfs clear them it locked up my SSH session, as well as subsequent sessions, it would allow me to initiate subsequent sessions (and authenticate), however would not deliver me to the prompt.  Additionally when I went onto the console if I ran a “zfs list, zpool list, or zpool status” it would lock up the shell every time.  When I say lock up, I mean lock up, no CTRL + C or Z or anything.  So since these devices were cache devices only this wasn’t the end of the world for us.

Now to get past the locked up shell, I simply removed the disks physically from the server, which allowed me to get my prompts back (I don’t recall if I had to CTRL + C, but I don’t think so.  Then I was able to zpool clear the devices to remove the FAULTED status and zpool offline them.  Also it is important to note, in our environment I am not aware of any “downtime” which we suffered due to this, it was simply the shells.  Our CIFS was still serving, as well as our NFS, we aren’t hosting any Fibre Channel on this one yet, but I would suspect that would not have been affected either.

# zpool status
pool: rpool
state: ONLINE
scan: resilvered 19.6G in 0h6m with 0 errors on Wed Apr 20 17:07:19 2011

NAME                         STATE     READ WRITE CKSUM
rpool                        ONLINE       0     0     0
mirror-0                   ONLINE       0     0     0
c0t5000C500339B1447d0s0  ONLINE       0     0     0
c0t5000C500339AFB37d0s0  ONLINE       0     0     0

errors: No known data errors

pool: tank
state: ONLINE
scan: scrub repaired 0 in 0h0m with 0 errors on Wed May 11 15:20:40 2011

NAME                       STATE     READ WRITE CKSUM
tank                       ONLINE       0     0     0
raidz1-0                 ONLINE       0     0     0
c0t5000C50033D5E9AFd0  ONLINE       0     0     0
c0t5000C50033D60E4Bd0  ONLINE       0     0     0
c0t5000C50033D62FC3d0  ONLINE       0     0     0
c0t5000C500260B365Bd0  ONLINE       0     0     0
c0t5000C500260FB5BBd0  ONLINE       0     0     0
raidz1-1                 ONLINE       0     0     0
c0t5000C500262A1883d0  ONLINE       0     0     0
c0t5000C5002627A2BBd0  ONLINE       0     0     0
c0t5000C50026016D3Fd0  ONLINE       0     0     0
c0t5000C50026282A07d0  ONLINE       0     0     0
c0t5000C50026132717d0  ONLINE       0     0     0
c0t500A0751030437A3d0    FAULTED      1    65     0  too many errors
c0t500A075103043823d0    FAULTED      0   124     0  too many errors

errors: No known data errors

However this did not solve the problem.  As of right now it appears that this problem was caused by a firmware bug.  The drives we had came with “Firmware Rev: 0001” with the latest version being 0002.  So if we inspect the changelog…

Release Date: 06/8/2011
Change Log:

  • Added margin to already-passing electromagnetic interference regulatory tests. Provides additional EMI margin for systems integrators.
  • Improved performance with Link Power Management. Resolves performance pauses and hesitations with certain host systems.
  • This is a recommended but not required firmware update. If the end user is experiencing pauses or hesitations in systems with Link Power Management (“LPM”) enabled, then this update is highly recommended.

Now here is what we were looking for.  Above I highlighted “pauses or hesitations” this is the problem, these pauses or hesitations cause read/write failures.  This is exactly the same reason why hardware RAID + ZFS is a bad thing.  So a firmware update was in order.  The great news about this firmware is that it comes with a really small Linux LiveCD which detects the disks and does the firmware update really quickly.  Read the guide that Crucial provided because there are some BIOS changes that will need to be made on the system where you are installing the Firmware to the drives (not your ZFS system), I used a spare desktop.

Also save yourself the heartache in the future, since Crucial was so nice to put the firmware revision on the sticker, it would be wise to update the sticker on yours, I used our label maker.  That way if you have to go to rev 3 or 16 or whatever you know where you are in case there is a requirement for you to upgrade through certain versions.

The most ironic thing of the whole situation is that we just got support for this box a few days before this happened, didn’t need to use it this time.

If you have also experienced this or a similar issue please leave a comment and tell me about it.


The Crucial M4 SSDs have another more critical firmware bug.  Read more here.

4 thoughts on “Adventures in ZFS: Faulted Cache Devices

  1. Shawn Jones

    I have a somewhat similar issue with my Acard ANS-9010 SSD RAM drive, thankfully it doesn’t lock my system. However, upon a reboot this device which has 16GB of RAM always comes up faulted. It’s more of an annoyance since I usually just have to remove it from the pool and then re-add it. I haven’t found a solution yet.

  2. matthew.mattoon Post author

    Hi Shawn,

    I just read up on the Acard ANS-9010, it is some sort of device in which you insert actual RAM into, and the system can use it as a kind of disk.

    Honestly I would not use this type of disk for this purpose.

    1) If you are going to buy RAM, then I would use it as RAM. RAM is very fast, SATA not so much, so basically you are paying full price for RAM that you cannot use fully.
    2) If you instead used that RAM as RAM, this would increase the size of the systems ARC (Advanced Read Cache) which is the first level of caching. When you add it as a cache device you end up putting it in the L2ARC (Level 2 Advanced Read Cache).
    3) A true SSD will give you much more storage at a much more friendly price point, for example your device costs $600USD+ on the manufacturers site, with no RAM included (so in other words 0GB). For less than $300USD you can get a 128GB SATA3 SSD (Crucial M4 is what I priced).
    4) And finally I wouldn’t even know where to begin on getting support for an issue like you are having. Basically it must have a firmware issue that would need to be fixed for it to be usable as a cache device, though it is possible that it just takes too much time for the storage to be initialized for the zpool to be able to use it from boot.

    Also FYI try a ‘zpool clear’ against the cache device, it should clear the fault without having to remove and re-add it to the device.

    Read up on the ARC and L2ARC and you’ll realize that this type of device really isn’t needed here, though I can think of alot of things where that would be gold.

    Also another note. If you do plan on using this device, make sure you are not using it as a ZIL, this would be dangerous for your data. Though it should be safe to use it as a cache device, just not very effective (but the worst case scenario is slower performance, with a ZIL it is data loss).


  3. John


    Does the drive work ok now, no pauses etc?

    I am thinking to use the m4 drives for my cache and ZIL, have been using F40 drives from corsair, in mirror, but one failed after two months…

  4. matthew.mattoon Post author


    The m4 works perfect after the firmware updates. No pauses or read write errors. As long as you mirror it the M4 ought to work fine as a ZIL (mirroring is needed for the ZIL regardless of hardware – due to the risk of data loss).