Home / server / Questions / 345718
Accepted
Timothy R. Butler
Asked: 2012-01-02 09:25:11 +0800 CST

ZFS Pool with Different Drive Sizes

  • 772

I am planning on setting up a FreeNAS ZFS pool using two 2 tb drives and two 1tb drives. I would like to have data redundancy somehow. I read this post which seems to suggest my two options are to lose 1tb per 2tb drive using RAIDZ or to use this command (which doubles the space required for data redundancy):

zfs set copies=2 poolname

Is there a better way to handle this and acheive something more like Drobo's Beyond RAID or Netgear's XRAID? Alternately, could I partition each 2tb drive into 1 tb partitions and put both partitions in the pool?

zfs truenas

3 Answers

  1. Best Answer

    There is a better way, create a single 3 TB pool composed of two mirrors.

    zpool create test mirror disk1 disk2 mirror disk3 disk4

    with disk1 and disk2 being the 1TB disks and disk3 and disk4 being the 2 TB ones.

    Edit:

    Should you want to maximize size and do not care that much about performance or best practices, you can partition all the drives with equal size partitions (or slices) and create a 4 TB hybrid pool with a 4 vdev RAIDZ and a 2 vdev mirror.

    zpool create -f test raidz d0p1 d1p1 d2p1 d3p1 mirror d0p2 d1p2

    Note the "-f" option required to force the command to accept the replication level mismatch.

    • 13

  2. This depends on how much data storage you need. You can create two pools of 1TB and 2TB each, using RAID 1. If not, see if you can acquire like-sized disks and try RAID 1+0 or RAIDZ.

    • 4

  3. From the ZFS admin guide:

    "The devices can be individual slices on a preformatted disk, or they can be entire disks that ZFS formats as a single large slice."

    So yes, you could create two 1-TB partitions on those 2TB drives, use them for RAID-Z vdev and the remaining space for non-redundant storage.

    However, according to the ZFS Best Practices Guide, you may experience degraded performance:

    For production systems, use whole disks rather than slices for storage pools for the following reasons:

    • Allows ZFS to enable the disk's write cache for those disks that have write caches. If you are using a RAID array with a non-volatile write cache, then this is less of an issue and slices as vdevs should still gain the benefit of the array's write cache.

    • For JBOD attached storage, having an enabled disk cache, allows some synchronous writes to be issued as multiple disk writes followed by a single cache flush allowing the disk controller to optimize I/O scheduling. Separately, for systems that lacks proper support for SATA NCQ or SCSI TCQ, having an enabled write cache allows the host to issue single I/O operation asynchronously from physical I/O.

    • The recovery process of replacing a failed disk is more complex when disks contain both ZFS and UFS file systems on slices.

    • 4