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Re: [Xen-users] Backup domU

Greg Woods wrote:

So after reading this (and taking a vacation), I did some more reading
and discovered that using "xm sysrq name-of-guest s" will cause the
guest to sync, assuming that the guest has been set up to allow this
(kernel.sysrq = 16 in the sysctl.conf file). So I tried syncing the
guest this way and then immediately taking a snapshot:

xm sysrq name-of-guest s; vm snap

("vm" is a script I wrote that sets up and mounts the snapshot, among
many other possible operations). This is going to create the snapshot as
soon after the sync as is realistically possible.

The /var/log/messages file on the guest shows that the sync did occur.
But if I run 'file' on the guest image from the snapshot, it still says
that the ext3 file system "needs journal recovery". So I am concerned
that I may still be getting a semi-corrupted image. Is there a way to be
certain that the image is clean? Is there a way to force the guest to
run the journal as well as syncing?

The only way to get a truly clean filesystem would be to close all files and unmount the volume (or at least remount it read only). As long as it's mounted r/w, then it's going to be dirty as far as any image/snapshot taken of it is concerned.

And as Javier Guerra Giraldez says, you still have the issue of what any applications might not have actually written to disk - if it's still in the application cache then it's not going to be written by an OS level sync.

Simon Hobson

Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
Christmas stocking fillers. Some available as e-books.

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