Re: [Xen-users] Backup domU

[Simon Hobson <linux@xxxxxxxxxxxxxxxx>]

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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