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

[John Madden <jmadden@xxxxxxxxxxx>]

>  > 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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