[linux-lvm] Q: LVM over RAID, or plain disks? A:"Yes" = best of both worlds?
philip at turmel.org
Tue Nov 30 13:13:00 UTC 2010
Hi Hans, (?)
On 11/30/2010 02:34 AM, hansbkk at gmail.com wrote:
> On Tue, Nov 30, 2010 at 2:14 PM, Nataraj <incoming-centos at rjl.com> wrote:
>>> TopRAID1's LVM is likely to be running over a RAID6 set , so I'm not
>>> depending on the TopRAID mirroring for reliability, just using it for
>>> the above volume cloning.
>> Your raid 1 backups won't mirror any snapshots of your LV's unless you
>> specifically setup mirroring of the snapshots after they exist.
> Ah, getting clearer to me, I was thinking I'd be mirroring the LV
> itself, but you're right, taking a snapshot and mirroring that is a
> much better idea.
I think you are making this overly complex, insisting on a RAID1 operation to backup from on filer to the other. Consider having each disk on filer #2 configured as a single LVM PV/VG, so it can stand alone in a rotation. The try the alternate below.
> So here's a summary of steps, please confirm:
> - create a snapshot of a given volume
Here's where you are over-complicating things:
> - create a new RAID1 mdN between that and a physical partition (blank?)
> - let that get sync'd up
> - break the RAID (fail the partition?), remove the drive
As an alternate, with simpler recovery semantics:
Create matching LV on non-RAID PV/VG on filer #2
dd + netcat + dd or other technique to dup the snapshot on filer #1 to filer #2
> - delete the snapshot
Now, you have a single disk in your backup set that can be mounted on either filer, and either copied back into service, or in an emergency, used directly (live) in filer #1.
This approach also gives you the *option* to implement the backup transfer with file system conversions, compression, free space removal, or any other administrative adjustments you need. A RAID mirror can only duplicate the raw block device.
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