I've been migrating a zfs raidz pool on linux to new discs via virtual devices which were sparse files. I've used partitions on the discs as the discs are different sizes of 1.9T each. The last disc to add is a 4Tb disc and I partitioned it as the others with a 1.9T partition to add to the pool. It's using a GPT partition table. When I try to replace the last file with the 1.9T partition on the 4T disc I get the following

zpool replace -f zfs_raid /zfs_jbod/zfs_raid/zfs.2 /dev/sdd1 
cannot replace /zfs_jbod/zfs_raid/zfs.2 with /dev/sdd1: devices have different sector alignment

How can I change the partition sector size to be 512 like the others, or failing that is it possible to change the other pool devices to 4024 ? Apparently the logical sector sizes are all 512

cat /sys/block/sdd/queue/hw_sector_size
Disk /dev/sdd: 4000.8 GB, 4000787030016 bytes, 7814037168 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes

As I have repartitioned the disc that contained the original 4th file based device that I'm trying to replace but it didn't work, I recreated the device file so it's currently resilvering that.

zpool status output:

NAME                            STATE     READ WRITE CKSUM
zfs_raid                        DEGRADED     0     0     0
  raidz1-0                      DEGRADED     0     0     0
    sda3                        ONLINE       0     0     0
    sdc2                        ONLINE       0     0     0
    sdb1                        ONLINE       0     0     0
    replacing-3                 OFFLINE      0     0     0
      /zfs_jbod/zfs_raid/zfs.2  OFFLINE      0     0     0
      /mnt/butter2/zfs.4        ONLINE       0     0     0  (resilvering)
  • Can't you do instead zfs attach zfs_raid <file> <device> and after sync zfs detach zfs_raid <file>
    – BitsOfNix
    Sep 11, 2013 at 7:25
  • wouldn't attaching a 5th device expand the array irreversibly? or maybe you mean something like adding a spare?
    – barrymac
    Sep 12, 2013 at 11:05
  • Not adding a spare or add new disk, doing zpool attach pool old_device new_device, this will mirror the old_device to the new_device, then you detach the old_device from your mirror after resilver: docs.oracle.com/cd/E26502_01/html/E29007/gayrd.html#scrolltoc <- info about attach/detach and the differences between add and attach.
    – BitsOfNix
    Sep 12, 2013 at 12:05
  • That did look promising by unfortunately returned a "cannot attach /dev/sdd1 to /zfs_jbod/zfs_raid/zfs.2: can only attach to mirrors and top-level disks"
    – barrymac
    Sep 12, 2013 at 13:25
  • Could you put your current zpool status zfs_raid output, to see the raid layout?
    – BitsOfNix
    Sep 12, 2013 at 13:38

1 Answer 1


I found the necessary option! the pool is currently resilvering the new partition after issuing the following command:

 zpool replace  -o ashift=9 zfs_raid <virtual device> /dev/sdd1

Although this is possible , it's not advisable because you get terrible performance by forcing a 4k type drive to be written as a 512b. I have learned the hard way that one should add

-o ashift=12 

when creating the pool to avoid having to recreate it later as it's currently not possible to 'migrate' to the 4k sector size.

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