{{tag>[archlinux kvm recover space]}}

=====Archlinux - KVM Recover space from VM=====
Note: A VM image on NFS storage might not work. I had success with local and iSCSI storage.
====Create VM====
  * Create VM with virtio-scsi controler and unmap setting: <code>--disk path=$IMAGEFILE,format=qcow2,bus=scsi,discard=unmap \
--controller scsi,model=virtio-scsi \
</code>
  * Note, use 'sda' in kickstart script, instead of 'vda'.
  * Check if trim is supported: <code>$ grep "" /sys/block/sda/queue/discard_*
/sys/block/sda/queue/discard_granularity:4096
/sys/block/sda/queue/discard_max_bytes:1073741824
/sys/block/sda/queue/discard_zeroes_data:0

$ cat /sys/block/sda/device/scsi_disk/*/provisioning_mode
unmap

</code>

====Configure discard====
  * Add discard option to /etc/fstab, or schedule fstrim operation.
  * Configure /etc/lvm/lvm.conf: <code>issue_discards = 1</code>
  * reboot

====Test====
  * Monitor VM image size. Use the -s ls option to see real usage.
  * Create large file: <code>cd /var/tmp/
time dd if=/dev/urandom of=tstfile bs=2048k count=512 oflag=direct</code>
  * Delete tstfile
  * Trim the filesystem: <code>fstrim -v /var</code>
  * Check VM image size. You can see in the first column the size grow and shrink after fstrim. <code>$ ls -ls vmcentos.qcow2
1226824 -rw-r--r-- 1 nobody kvm 1256325120 Dec  2 21:59 vmcentos.qcow2
1355912 -rw-r--r-- 1 nobody kvm 1388511232 Dec  2 21:59 vmcentos.qcow2
1552968 -rw-r--r-- 1 nobody kvm 1589837824 Dec  2 21:59 vmcentos.qcow2
1755128 -rw-r--r-- 1 nobody kvm 1796943872 Dec  2 22:00 vmcentos.qcow2
1949832 -rw-r--r-- 1 nobody kvm 1996685312 Dec  2 22:00 vmcentos.qcow2
2156152 -rw-r--r-- 1 nobody kvm 2207477760 Dec  2 22:00 vmcentos.qcow2
2245256 -rw-r--r-- 1 nobody kvm 2299199488 Dec  2 22:00 vmcentos.qcow2
2245256 -rw-r--r-- 1 nobody kvm 2299199488 Dec  2 22:00 vmcentos.qcow2
2245256 -rw-r--r-- 1 nobody kvm 2299199488 Dec  2 22:00 vmcentos.qcow2
2245256 -rw-r--r-- 1 nobody kvm 2299199488 Dec  2 22:00 vmcentos.qcow2
2245256 -rw-r--r-- 1 nobody kvm 2299199488 Dec  2 22:00 vmcentos.qcow2
1130376 -rw-r--r-- 1 nobody kvm 2299199488 Dec  2 22:00 vmcentos.qcow2
1130376 -rw-r--r-- 1 nobody kvm 2299199488 Dec  2 22:00 vmcentos.qcow2
1130376 -rw-r--r-- 1 nobody kvm 2299199488 Dec  2 22:00 vmcentos.qcow2
1130376 -rw-r--r-- 1 nobody kvm 2299199488 Dec  2 22:00 vmcentos.qcow2</code>