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Re: [Xen-users] software raid (mdadm) with a local partition and a nbd d

To: Tomoki Taniguchi <tomoki.taniguchi@xxxxxxxxx>
Subject: Re: [Xen-users] software raid (mdadm) with a local partition and a nbd device.
From: Morten Bøgeskov <xen-users@xxxxxxxxxxxxxxxxxx>
Date: Tue, 13 Nov 2007 08:31:34 +0100
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I've previously made a redundant iscsi-target with this: http://www.drbd.org/ because-i-could(tm). I didn't really have any useful reason (and both ran inside domU's on the same machine), but after some fiddling I got it up and running.

I don't recall if I ran LVM on the iscsi-target (http://iscsitarget.sourceforge.net/) side or the iscsi-client (http://www.open-iscsi.org/) side (client side I think), but it should be doable at both ends. If you insist on running nbd I don't see why that shouldn't work. And you could run directly on the /dev/rdbdX, if you use your xen-machine as one of the drbd servers.


Quoting Tomoki Taniguchi <tomoki.taniguchi@xxxxxxxxx>:

I have a Fileserver serving out LVM partitions as domU disks
using nbd. but since the file server is not redundant, I still
have a single point of failure.  So if my Fileserver crashes,
all my domUs on various dom0s will crash all at once.

I want to avoid this situation.  I am thinking maybe I could
alleviate this problem by setting up the nbd device with a local LVM
lv partition
as a raid 1 device.  that way if the fileserver fails and the nbd
device becomes unavailable,
then the domUs will keep writing to the local LV partition until the
ndb device is back online
and caches up.

Is this possible?

in the case this dom0 fails, start the domU on another dom0 and have
the raid 1 catch up
on that machine using the nbd device ?


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