RE: [Xen-users] iSCSI Volumes and Xen

[Jeff Sturm <jeff.sturm@xxxxxxxxxx>]

> -----Original Message-----
> From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx [mailto:xen-users-
> bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of John Madden
> Sent: Thursday, January 14, 2010 11:07 AM
> To: matt@xxxxxxxxxxxxxxxxxx
> Cc: xen-users@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [Xen-users] iSCSI Volumes and Xen
> 
> > Is the only backup option for a running domU to run a conventional
backup
> > client within it, such as bacula?
> 
> If it were my data, I'd do conventional backups.  Others here report
> success with snapshots, however, so I'll let them chime in.  I've
never
> looked into the xm save/restore stuff.
> 

My take:  Snapshots aren't backups, and backups aren't snapshots.  Both
are useful but neither completely takes the place of the other.

Any storage strategy should be tailored to the circumstances.  I've been
taking frequent (dirty) snapshots on all our development systems for a
while--they are cheap and easy, and completely nonintrusive.  I've never
attempted to use one of these snapshots to get a full system restore,
but I have used them on occasion when a developer was a little
overzealous with "rm -rf" and then asked: "Any chance I can get these
file(s) back?"

Mounting ext3 snapshots, even when dirty, seems to work fine.

Full system backups are best done when a host is down.  Any kind of safe
online backup is application-dependent--for example, I think MySQL can
be configured for synchronous writes of tablespace and binlog data,
allowing for point-in-time recovery from a LVM snapshot.  But I haven't
tried it, and please don't take my word for it.

Certain filesystems support a "freeze" option, like GFS, that
theoretically would help to obtain a consistent snapshot, but that
probably only checkpoints buffers and journals, and certainly doesn't
guarantee the state of any files open for writing by applications.

In summary, I'll keep my snapshots, but don't have any illusion that
they are a substitute for regular backups.

-Jeff



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