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This chapter is from the book

This chapter is from the book

2.9 Example of a Misconfigured Pool

The following is an example of a ZFS pool that started as a RAID-Z pool and needed more space. The administrator just added the new disks to the pool. The status output follows.

$ zpool status -v
pool: mypool
state: ONLINE
status: One or more devices has experienced an error resulting in data
corruption.  Applications may be affected.
action: Restore the file in question if possible.  Otherwise restore the entire pool
from backup.
see: http://www.sun.com/msg/ZFS-8000-8A
scrub: resilver completed with 0 errors on Tue Nov 18 17:05:10 2008

mypool      ONLINE       0     0    18
  raidz1    ONLINE       0     0     0
    c2t0d0  ONLINE       0     0     0
    c2t1d0  ONLINE       0     0     0
    c2t2d0  ONLINE       0     0     0
    c2t3d0  ONLINE       0     0     0
    c2t4d0  ONLINE       0     0     0
    c2t5d0  ONLINE       0     0     0
  c2t9d0    ONLINE       0     0     0
  c2t11d0   ONLINE       0     0     0
  c2t12d0   ONLINE       0     0    18
  c2t10d0   ONLINE       0     0     0
  c2t13d0   ONLINE       0     0     0
  c2t8d0    AVAIL

errors: Permanent errors have been detected in the following files:


c2t9d0, c2t10d0, c2t11d0, c2t12d0, and c2t13d0 are single-disk vdevs. They have no redundancy. The spare vdev will not help because there is nothing to resilver with when one of the single-disk vdevs fails. In this case, ZFS has detected permanent errors in mypool/dataset/u01 and has suggested an action of restoring the files from backup or restoring the whole pool from backup.

The ZFS pool is in danger of a single disk failure that may destroy the whole pool. The only way to get this pool to be redundant is to mirror all the single-vdev drives.

Figure 2.7 represents the ZFS pool mypool. The figure shows five single-disk vdevs with a single RAID-Z vdev. Any damage to the single disks will cause ZFS to lose data, or, worse, the pool will fail.

Figure 2.7

Figure 2.7 The ZFS pool mypool has a single RAID-Z vdev and five single-disk vdevs

You can correct this configuration for pool redundancy in two ways:

  • If there are enough disks, you can mirror the single-disk vdevs.
  • You can back up all the file systems and re-create the pool. Then do a full restore of the file systems.

The procedure to replace a single-disk vdev in the preceding example is to mirror the drive in question and then detach the bad drive. What follows is the command-line procedure:

  1. Mirror the drive with bad sector problems:
    # zpool replace mypool <baddisk> <gooddisk>
  2. Detach the bad disk:
    # zpool detach mypool <baddisk>
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