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Re: [Xen-users] A simple backup

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Subject: Re: [Xen-users] A simple backup
From: "Fajar A. Nugraha" <fajar@xxxxxxxxx>
Date: Fri, 09 May 2008 08:36:22 +0700
Cc: Steve Spencer <sspencer@xxxxxxxx>
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Mark Williamson wrote:
When you take an atomic snapshot of a domU's state, it's much the same kind of backup image as you'd get by yanking the power from a server, removing its hard drive and copying it byte-for-byte - often readable but definitely not clean. That consistency problem is what makes it impossible to guarantee that such backups are definitely readable.

Hi Mark,

Some thoughts about your comment.
In our environment, one of the requirements for the OS and applications is that it must be able to recover quickly and cleanly from a power failure. This is actually one of the reasons why we're starting to migrate some stuff to zfs : because, when used properly, it always guarantee filesystem consistency in the event of power failure.

IMHO, even the best commercial SAN-based backup solution uses that assumption, so for practical purposes, atomic backup for domU's storage should be sufficient.

It would be nicer if you could somehow guarantee a consistent filesystem state on your disk snapshot. I've been looking into how to do this and I believe it's quite possible to modify the code to support this properly.

It would be interesting if you can make it happen.



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