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Re: [linux-lvm] mirror and snapshot incompatible



For production environment I guess I'll switch to md+lvm for mirroring so that I'll be able to safely snapshot the mirrored fs. I'll keep playing with devmapper mirror combined with snapshot (without lvm) and report if it misbehaves. So far it hasn't, but I only did some limited experiments. I hope some future version of lvm will add support for this combination.

   Yoav

Jonathan Brassow wrote:
No, there isn't a reason LVM prevents it, other than we haven't gotten to it yet. That being said... because we haven't gotten to it yet also means there probably hasn't been a whole lot of testing of such a configuration. Therefore, it's difficult to quantify the safety.

 brassow

On Oct 28, 2008, at 7:32 PM, Yoav wrote:

I know how to do it through device-mapper. I'm just worried that maybe there's a reason why lvm prevents it. Are you aware of such reason, or is it safe?

Jonathan Brassow wrote:
It is possible to do all the things you are asking through device-mapper... but there is no easy way to do it. (and LVM does not yet have the capabilities to manage this yet either.)

brassow

On Oct 27, 2008, at 9:28 PM, Yoav wrote:

According to lvcreate, a snapshot of a mirrored volume cannot be created ("Snapshots and mirrors may not yet be mixed"). However, devmapper does not seem to have the same limitation when used directly (not through lvm).

Is there a current reason for lvcreate to enforce this rather harsh limitation?

What are the risks I'm taking by manually creating a dm-snapshot from a dm-mirror device? (of course I'm also replacing the dm-mirror device with a snapshot-origin of the actual dm-mirror device).

If there is an actual reason for preventing this, what is the suggested way to consistently backup a mirror volume? Is there a way to temporarily take one of the mirror "legs" (mimage devices) offline in order to back it up, and resync it later?

 Yoav

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read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/

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https://www.redhat.com/mailman/listinfo/linux-lvm
read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/

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https://www.redhat.com/mailman/listinfo/linux-lvm
read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/


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