Its not just the tap2:remus:....

there is a bug lurking in the in tools/python/xen/remus/device.py in ReplicatedDisk class. The regular expression scans the domU config for only tap:tapdisk:remus... or tap:remus.. disk types only. I was able to get it working by fixing that regexp.
This applies for xen 4.0.1 only. Am not sure about xen unstable.
Here is a patch that might be of help to you (its rather crude but heck I was too lazy :) )
diff -r b536ebfba183 tools/python/xen/remus/device.py
--- a/tools/python/xen/remus/device.py Wed Aug 25 09:22:42 2010 +0100
+++ b/tools/python/xen/remus/device.py Fri Sep 03 08:47:13 2010 -0700
@@ -36,10 +36,13 @@
         # to request commits.
         self.ctlfd = None

-        if not disk.uname.startswith('tap:remus:') and not disk.uname.startswith('tap:tapdisk:remus:'):
+        if not disk.uname.startswith('tap2:remus:') and not disk.uname.startswith('tap:remus:') and not disk.uname.startswith('tap:tapdisk:remus:'):
             raise ReplicatedDiskException('Disk is not replicated: %s' %
                                         str(disk))
-        fifo = re.match("tap:.*(remus.*)\|", disk.uname).group(1).replace(':', '_')
+        if disk.uname.startswith('tap2:remus:'):
+            fifo = re.match("tap2:.*(remus.*)\|", disk.uname).group(1).replace(':', '_')
+        else:
+            fifo = re.match("tap:.*(remus.*)\|", disk.uname).group(1).replace(':', '_')
         absfifo = os.path.join(self.FIFODIR, fifo)
         absmsgfifo = absfifo + '.msg'

On Tue, Sep 7, 2010 at 11:01 PM, Pasi Kärkkäinen <pasik@iki.fi> wrote:

On Tue, Sep 07, 2010 at 03:28:32PM -0700, Jonathan Kirsch wrote:
> Hello,
>
> I have been playing around with Remus on Xen 4.0.1, attempting to
> fail-over for an HVM domU.
>
> I've run into some problems that I think could be related to tapdisk2 and
> its interaction with how one sets up Remus disk replication in the domU
> config file.
>
> A few things I've noticed:
>
> -The tap:remus:backupHostIP:port|aio:imagePath notation does not work for
> me, although this is what is written in the Remus documentation. However,
> I have found the following to work (i.e., not complain when starting
> domU), so this is what I've been using:
>
> tap2:remus:backupHostIP:port|aio:imagePath...
>

Yeah, this stuff was changed in Xen 4.0.1:
http://wiki.xensource.com/xenwiki/blktap2

I guess someone should update the remus wiki page.

-- Pasi

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