Checking ASHIFT On Existing Pools
So I have an existing pool that was created several years ago on an old build of FreeNAS, and I wanted to check and see if the ashift was set correctly for 4K, meaning I want an ashift=12 (2^12=4096). What does a quick Google tell me to do?
[root@server] ~# zpool get all | grep ashift
[root@server] ~#Huh… nothing. That’s odd.
[root@server] ~# zpool get all
NAME PROPERTY VALUE SOURCE
Array1 size 2.72T -
Array1 capacity 13% -
Array1 altroot /mnt local
Array1 health ONLINE -
Array1 guid 4640375899101559431 default
Array1 version - default
Array1 bootfs - default
Array1 delegation on default
Array1 autoreplace off default
Array1 cachefile /data/zfs/zpool.cache local
Array1 failmode continue local
Array1 listsnapshots off default
Array1 autoexpand on local
Array1 dedupditto 0 default
Array1 dedupratio 1.00x -
Array1 free 2.36T -
Array1 allocated 364G -
Array1 readonly off -
Array1 comment - default
Array1 expandsize - -
Array1 freeing 0 default
Array1 fragmentation 12% -
Array1 leaked 0 default
Array1 feature@async_destroy enabled local
Array1 feature@empty_bpobj active local
Array1 feature@lz4_compress active local
Array1 feature@multi_vdev_crash_dump enabled local
Array1 feature@spacemap_histogram active local
Array1 feature@enabled_txg active local
Array1 feature@hole_birth active local
Array1 feature@extensible_dataset enabled local
Array1 feature@embedded_data disabled local
Array1 feature@bookmarks enabled local
Array1 feature@filesystem_limits disabled local
Array1 feature@large_blocks disabled local
freenas-boot size 14.2G -
freenas-boot capacity 5% -
freenas-boot altroot - default
freenas-boot health ONLINE -
freenas-boot guid 11011409209729808822 default
freenas-boot version - default
freenas-boot bootfs freenas-boot/ROOT/9.10-STABLE-201604261518 local
freenas-boot delegation on default
freenas-boot autoreplace off default
freenas-boot cachefile - default
freenas-boot failmode wait default
freenas-boot listsnapshots off default
freenas-boot autoexpand off default
freenas-boot dedupditto 0 default
freenas-boot dedupratio 1.00x -
freenas-boot free 13.5G -
freenas-boot allocated 773M -
freenas-boot readonly off -
freenas-boot comment - default
freenas-boot expandsize - -
freenas-boot freeing 0 default
freenas-boot fragmentation - -
freenas-boot leaked 0 default
freenas-boot feature@async_destroy enabled local
freenas-boot feature@empty_bpobj active local
freenas-boot feature@lz4_compress active local
freenas-boot feature@multi_vdev_crash_dump disabled local
freenas-boot feature@spacemap_histogram disabled local
freenas-boot feature@enabled_txg disabled local
freenas-boot feature@hole_birth disabled local
freenas-boot feature@extensible_dataset disabled local
freenas-boot feature@embedded_data disabled local
freenas-boot feature@bookmarks disabled local
freenas-boot feature@filesystem_limits disabled local
freenas-boot feature@large_blocks disabled localLooking at just the zpool get all output, looks like the ashift attribute is missing. I’m guessing that the ashift attribute wasn’t specified upon pool creation, leaving it up to the drive to report whether it is a 4K drive or not. Another round of Google reveals the zdb -C command. Let’s try that.
[root@server] ~# zdb -C | grep ashift
ashift: 9Huh. ashift=9 means 512… and that’s no good. But wait…
[root@server] ~# zdb -C
freenas-boot:
version: 5000
name: 'freenas-boot'
state: 0
txg: 95367
pool_guid: 11011409209729808822
hostid: 2882373074
hostname: ''
vdev_children: 1
vdev_tree:
type: 'root'
id: 0
guid: 11011409209729808822
create_txg: 4
children[0]:
type: 'disk'
id: 0
guid: 14099280634272200775
path: '/dev/da0p2'
whole_disk: 1
metaslab_array: 30
metaslab_shift: 27
ashift: 9
asize: 15370551296
is_log: 0
create_txg: 4
features_for_read:zdb is only listing the USB boot drive. Back to Google and we get…
[root@server] ~# zdb -U /data/zfs/zpool.cache
Array1:
version: 5000
name: 'Array1'
state: 0
txg: 8520213
pool_guid: 4640375899101559431
hostid: 2882373074
hostname: 'server.workgroup'
vdev_children: 1
vdev_tree:
type: 'root'
id: 0
guid: 4640375899101559431
children[0]:
type: 'raidz'
id: 0
guid: 7207720561268687283
nparity: 1
metaslab_array: 35
metaslab_shift: 34
ashift: 12
asize: 2994157387776
is_log: 0
create_txg: 4
children[0]:
type: 'disk'
id: 0
guid: 2714791811722168437
path: '/dev/gptid/cca60fe6-5031-11e4-9120-001bb9ed2d38'
whole_disk: 1
DTL: 204
create_txg: 4
children[1]:
type: 'disk'
id: 1
guid: 6091442355483197824
path: '/dev/gptid/cd472cc3-5031-11e4-9120-001bb9ed2d38'
whole_disk: 1
DTL: 163
create_txg: 4
children[2]:
type: 'disk'
id: 2
guid: 1150763296991461133
path: '/dev/gptid/21338e8c-25ea-11e6-a898-3cd92b0298a8'
whole_disk: 1
DTL: 377
create_txg: 4
features_for_read:
com.delphix:hole_birthThere we go. Now let’s that down.
[root@server] ~# zdb -U /data/zfs/zpool.cache | grep ashift
ashift: 12And we have our answer.
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