Today the disks for my new ZFS NAS arrived, rejoice! 😍

Now I ask myself: If some day one of the drives fails, how am I supposed know which of the physical ones it is? My preliminary plan is to plug them into to disk container one by one, writing down the newly appearing blkids and labeling the corresponding drive. This is somewhat time consuming, so you folks have a better idea?


  • @asciiphil
    2 years ago

    One super-easy way to identify disks on the fly is just to do a cat </dev/sdx >/dev/null and see which disk activity light stays on.

    What I do is figure out which names in /dev/disk/by-path correspond to which disks. The by-path names are stable, even if you replace the disks (as long as the cabling doesn’t change). Then I set up aliases in /etc/zfs/vdev_id.conf to give the disks names that correspond to the external labels on the enclosure.

    For example, disk /dev/disk/by-path/pci-0000:06:08.0-sas-0x5842b2b2167fc188-lun-0 might be the disk in slot zero in the array I’ve designated as “array0”. So /etc/zfs/vdev_id.conf would have:

    alias  array0-0  pci-0000:06:08.0-sas-0x5842b2b2167fc188-lun-0

    Then I create the pool with the /dev/disk/by-vdev names so I can tell immediately what each disk is. (If you’ve already created the pool, you can export it and then use zpool import -d /dev/disk/by-vdev to switch to the vdev names.)

    In theory, you can use some other settings in /etc/zfs/vdev_id.conf to get the system to enumerate the disks itself, rather than working out the aliases by hand. In my case, my enclosures don’t have stable numbering that the automatic settings can work with.

    • @asciiphil
      2 years ago

      A rather more sophisticated way to identify a disk, if it’s in an enclosure that has ID LEDs, is to use sg_ses.

      The rough process for that is:

      • Run lsscsi -g to get the generic SCSI device (/dev/sgN) for the enclosure.
      • Run lsscsi -t to get the SAS address for a disk. (Not sure whether this will work if it’s a SATA enclosure; all of mine are SAS.)
      • Run sg_ses -p aes /dev/sgN | less, where /dev/sgN is the enclosure’s generic SCSI device. Look through the output to find the SAS address and, from that, get the index number of the disk.
      • Run sg_ses --set ident --index I /dev/sgN, where I is the disk index number and /dev/sgN is the enclosure’s device. This will turn on the ID LED for the disk.
      • Run sg_ses --clear ident --index I /dev/sgN to turn the LED off.

      You can also use fault instead of ident to turn on the “drive fault” LED, in case the enclosure has those but not ID LEDs.