Re: [Xen-users] Cheap and cheerful replication

[Alexandre Chapellon <a.chapellon@xxxxxxxxx>]

Le 06/06/2011 17:00, msgbox450@xxxxxxxxx a écrit :

Hi guys,

I wonder if anyone has found any simple solution for cheap and cheerful replication between two hosts (in this case for XCP)?

Basically I have two machines (A and B). I want to run 8 VMs on local storage on server A and 8 VMs on local storage on server B. I want all the machines on server A to be backed up to server B and vice versa. In the event of failure, I want to be able to run all 16 VMs on one host.

My current thought is to just set up NFS on both hosts and then set up nightly snapshots on each to copy to the other. However, it would be nice to have some proper block level replication going on instead so that live migration could be used.

This is what DRBD is meant for: networked block level replication
But maybe it's not so easy and some users here reported (unverified) issues. I f you don't feel confortable with cluster architectures forget about drbd it wouls lead you to data loss pretty surely.

Also be aware that block level replication *won't*  guarantee any filesystem consistancy. In most cases it's not a problem but if you have high rate IO (eg a busy postgresql or oracle sgbd) you may not be able to mount the replicated filesystems.

Knowing that you may also consider exporting you block device using nbd or gndb or aoe..., and mirror it to a local volumes using mdadm... that should work too.

What ever solutions you choose I don't think any of them would be "simple". Remote data replication *is* a complicated situation, and of course it won't replace backup systems.

regards.

Has anyone got any good ideas for this (and before anyone says it,  I don't want to involve any separate machines or network storage devices because that pushes the budget out of window, I want to find a way to make it work with a mirrored pair of hosts).

Thanks :D

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