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Re: [Xen-users] HA Xen on 2 servers!! No NFS, special hardware, DRBD or

To: chris@xxxxxxxxxx
Subject: Re: [Xen-users] HA Xen on 2 servers!! No NFS, special hardware, DRBD or iSCSI...
From: Eric Windisch <lists@xxxxxxxxxx>
Date: Wed, 07 Jun 2006 08:33:03 -0400
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a little while before I can find the time to try it.
3.) Is it reliable?  Should be; AoE is relatively new but very simple.  LVM is 
well-tested and
software mirroring is as old as the hills.


To confirm, you're talking about doing software raid within the DomU? If one of the devices drops out, no big deal? Interesting. The biggest problem here when one of the devices becomes desyncronized, such as after a temporary network failure, you will rewrite the entire secondary device.

I have been thinking of testing NBD for a similar setup, instead of AoE. My understanding is that NBD natively supports raid-1 mirroring with logic particularly useful for RAID-over-TCP. That is, during a normal active-sync it should work just like regular software raid, but when the volumes become desynchronized (such as after a crash), it will not rewrite the whole disk from scratch (as is common in raid-1) but will only update inconsistent blocks (sort of like rsync). NBD also supports Raid-5, btw.

Client-side RAID-1 of AoE devices will be problematic unless you use a driver modified in the above-described fashion. I'm not (currently) aware of a driver that will solve that for you (but I also haven't really looked).


--
Eric Windisch

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