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Re: [Xen-users] High availability and live migration with just LVMand ha

 > What's wrong with backing up from the clients?

You mean the guests? Well, it could be they get corrupted while for instance failing over because a xen host dies. Quickest restore path is then a snapshot restore and then a guest data restore.

If you're doing guest data restore once the guest is up, why bother with snapshots at all? (In other words, you can deploy VMs all day from a vanilla install process and then restore data, so snapshots don't really buy you anything.)

Wait a sec, so i still would have no snapshots? How is this achieved then with hvm guests?

Correct. I don't know how anyone accomplishes this or thinks that they do, none of it adds up as far as I'm concerned. If you want consistent backups, they have to happen either FROM the client or somehow in concert with it.

You wouldn't run fsck on a mounted filesystem, would you? Or assume that a 'dd if=/dev/sda' backup would be consistent while you were writing data to the disk, right? Well, taking snapshots "from the san" or "from dom0" without "letting the client know" is the same thing.

Do they need to be stopped for backups? Live migration still works, right? (Provided i have clvm)

LVM+cLVM is only one way to accomplish live migration. You can also do it with disk images stored on NFS or a clustered filesystem like OCFS2, for example. I happen to like LVM+cLVM because I prefer the nature and performance advantage of phy: disk assignment.

John




--
John Madden
Sr UNIX Systems Engineer
Ivy Tech Community College of Indiana
jmadden@xxxxxxxxxxx

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