Tag: linux

zfs snapshot sort by size

Posted on by mario

When you see your zpool exploding, but the “used” size isn’t that much, you may take a look at your snaphosts.

First find the dataset with the that has the largest snapshot

zfs list -o name,usedbysnapshots | sort -r -k2

example output

tank/mails                                  56.3G
tank/store                                   261M
tank/docker                                 2.38M

In this case the tank/mails dataset should be looked at.

Snapshots can then be listed for that filesystem by using a command

# zfs list -t snapshot -r 
zfs list -t snapshot -r tank/mails

ceph scrubbing time

Posted on by mario

When you don’t scrub your ceph pool it will scrub itself when you don’t want it to scrub: during working hours. To avoid that you can set the time in the night when scrubbing is allowed

the ceph config set is global for the cluster / all nodes.

root@pve-01:/etc/ceph# ceph config get osd osd_scrub_begin_hour
0
root@pve-01:/etc/ceph# ceph config set osd osd_scrub_begin_hour 22
root@pve-01:/etc/ceph# ceph config get osd osd_scrub_begin_hour
22
root@pve-01:/etc/ceph# ceph config get osd osd_scrub_end_hour
0
root@pve-01:/etc/ceph# ceph config set osd osd_scrub_end_hour 7
root@pve-01:/etc/ceph# ceph config get osd osd_scrub_end_hour
7
root@pve-01:/etc/ceph#

ZFS rename disk path

Posted on by mario
zpool status
  pool: tank
 state: ONLINE
config:

        NAME                                          STATE     READ WRITE CKSUM
        tank                                          ONLINE       0     0     0
          mirror-0                                    ONLINE       0     0     0
            usb-SanDisk_SDSSDA-1T00_0123456789CA-0:0  ONLINE       0     0     0
            da3p4                                     ONLINE       0     0     0

errors: No known data errors

zpool set path=/dev/disk-by-id/sdsdsdsd tank da3p4
zpool set path=/dev/gpt/my_nice_name

just type `zpool import` and you will see the name that you can import.

if you want to change the mount path use

zpool import -R /other/path poolname

to rename the pool use

zpool import original_name new_name

zfs volume

Posted on by mario
zfs create -V 10G tank/virtualdisk
mkfs.ext4 /dev/zvol/fourth/virtualdisk
zfs set compression=on fourth/virtualdisk

To create a sparse volume you add the -s parameter so that the previous command would look like this

Sparse = volume with no reservation / Thin provisioning

zfs create -s -V 10G fourth/virtualdisk

mount /dev/zvol/fourth/virtualdisk /mnt

Check available space on the filesystem:

df -h /mnt

Resize

zfs set volsize=20G tank/virtualdisk
resize2fs /dev/zvol/tank/virtualdisk
df -h /mnt
zfs list

As mentioned, even if the volume is empty at the moment, space is preallocated, so it takes 20GB out of our pool. But even though it wasn’t initially created as a sparse volume, we can change it now

zfs set refreservation=none tank/virtualdisk
zfs list

Tip: when using ext4 on a ZFS volume, you may notice that after deleting data in `/mnt`, the volume doesn’t reflect any gains in usable space. This is because, for efficiency, a lot of filesystems like ext4 don’t actually remove the data on disk, they just dereference it. Otherwise, deleting 100GB of information would take a very long time and make your system slow. This means that deleted files continue to exist in random blocks on disk, consequently on the ZFS volume too. To free up space, you would use a command such as `fstrim /mnt` to actually erase unused data in the ext4 filesystem. Only use the tool when needed, as to not “tire” the physical devices unnecessarily (although the numbers are pretty high these days, devices have a limited number of write cycles).

Don’t forget that a lot of the other ZFS-specific features are also available on volumes (e.g snapshots and clones).

Posts Tagged linux

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