[libvirt-users] Re: fsck and guest images

[Nicolas Sebrecht]

The 03/07/13, Jamie Fargen wrote:

> Hey!
> 
> I have some RHEL6 hypervisors and the VMs are in raw qemu image files in a
> local raid array linux raid + lvm + ext3. When a kernel update is installed
> a reboot is necessary, usually it has been more than 180 days since the
> last reboot and the file system is fsck'd and this takes 2-3 hours.
> 
> I am curious to know if there is any documentation that addresses the pro's
> and con's of fsck'ing the volume containing /var/lib/libvirt/images.

This is standard ext fsck to prevent errors after some time.

In order to avoid long fsck times, we use ext4 almost everywhere (for
both hypervisors and guests). I would suggest you to switch to a newer
filesystem supporting fast fsck.

> Could fsck make a change to the underlying file system that the guest
> images are stored on, which the guest operating system may not be able to
> handle when it runs its own file system maintenance, i.e. fsck or chkdsk.

Talking about filesystems errors, you should assume that everything is
possible. Though, the fsck on /var/lib/libvirt/images is limited to the
filesystem used by the hypervisor and should not interfere with the
filesystems of the guests. An exception I'm aware of is a reiserfs
filesystem inside another reiserfs filesystem (/var/lib/libvirt/images
is reiserfs and the guests are in reiserfs, too).

> Is file system maintenance on the hypervisor volume storing the VM images
> redundant to the VM's own file system consistancy utilities.

As said above, it's not redondant. The fsck at hypervisor level keeps
limited to the filesystem at hypervisor level.

Regards,

-- 
Nicolas Sebrecht