Zpool (2-mirror) with mixed ashift

[Vladislav V. Prodan]

Hi all!

I have the misfortune. :(
I had a system with two HDD with a cluster size of 512b.
Due to lack of space in the system, it was decided to put the 4 3TB HDD
in 2-mirror zfs pool
I used the instructions from the forum:
http://forums.freebsd.org/showthread.php?t=37819
But with the addition of the second mirror and the second mirror turned
out to ashift = 9.
Notice now zfs pool filled with more than 50%
How can I safely do a second mirror in the pool ashift=12 without losing
data?
How to continue to create 2-mirror zfs pool for 4k HDD?

Thank you.
A little more than further information:

FreeBSD 9.1-STABLE #0 r251351M: Sat Jun 15 01:22:15 EEST 2013    amd64

# zpool list tank
NAME   SIZE  ALLOC   FREE    CAP  DEDUP  HEALTH  ALTROOT
tank  5,44T  3,23T  2,21T    59%  1.16x  ONLINE  -

# zfs list tank
NAME   USED  AVAIL  REFER  MOUNTPOINT
tank  3,41T  2,12T   186K  /tank

# zpool status
  pool: tank
 state: ONLINE
  scan: resilvered 2,38T in 8h46m with 0 errors on Mon Jun 17 02:32:29 2013
config:

        NAME           STATE     READ WRITE CKSUM
        tank           ONLINE       0     0     0
          mirror-0     ONLINE       0     0     0
            gpt/disk3  ONLINE       0     0     0
            gpt/disk4  ONLINE       0     0     0
          mirror-1     ONLINE       0     0     0
            gpt/disk0  ONLINE       0     0     0
            gpt/disk1  ONLINE       0     0     0

errors: No known data errors


# zdb
tank:
    version: 5000
    name: 'tank'
    state: 0
    txg: 47135
    pool_guid: 13092523331396101530
    hostid: 143250101
    hostname: 'mary-teresa.XXXXX.ua'
    vdev_children: 2
    vdev_tree:
        type: 'root'
        id: 0
        guid: 13092523331396101530
        children[0]:
            type: 'mirror'
            id: 0
            guid: 3335739818
            whole_disk: 0
            metaslab_array: 34
            metaslab_shift: 34
            ashift: 12
            asize: 3000586993664
            is_log: 0
            create_txg: 4
            children[0]:
                type: 'disk'
                id: 0
                guid: 11030443378289800725
                path: '/dev/gpt/disk3'
                phys_path: '/dev/gpt/disk3'
                whole_disk: 1
                DTL: 39
                create_txg: 4
            children[1]:
                type: 'disk'
                id: 1
                guid: 11332687226484843334
                path: '/dev/gpt/disk4'
                phys_path: '/dev/gpt/disk4'
                whole_disk: 1
                DTL: 24
                create_txg: 4
                resilvering: 1
        children[1]:
            type: 'mirror'
            id: 1
            guid: 17121080319583017092
            metaslab_array: 38
            metaslab_shift: 34
            ashift: 9
            asize: 3000586993664
            is_log: 0
            create_txg: 47133
            children[0]:
                type: 'disk'
                id: 0
                guid: 4425616934581567964
                path: '/dev/gpt/disk0'
                phys_path: '/dev/gpt/disk0'
                whole_disk: 1
                create_txg: 47133
            children[1]:
                type: 'disk'
                id: 1
                guid: 5113772130885677504
                path: '/dev/gpt/disk1'
                phys_path: '/dev/gpt/disk1'
                whole_disk: 1
                create_txg: 47133
    features_for_read:



-- 
Vladislav V. Prodan
System & Network Administrator
http://support.od.ua
+380 67 4584408, +380 99 4060508
VVP88-RIPE