# 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 local ``` Looking 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: 9 ``` Huh. `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_birth ``` There we go. Now let’s that down. ``` [root@server] ~# zdb -U /data/zfs/zpool.cache | grep ashift ashift: 12 ``` And we have our answer. [Original Article](https://wikipedia.mutschlerhome.com/attachments/22)