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Re: Re: [Xen-users] tap:aio not working...

To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: Re: Re: [Xen-users] tap:aio not working...
From: Gernot Kieseritzky <gernotk@xxxxxxxxx>
Date: Wed, 30 Apr 2008 13:06:01 +0200
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> Nick Couchman schrieb:
>> > I'm running SLES10 SP1 and have been using file:/ for my file-backed 
>> > domUs.  The domUs sit on a shared OCFS2 SAN-backed filesystem and are run 
>> > on my three or four XEN servers.  I'm having issues with the loopback 
>> > devices not being released when the domUs shutdown or migrate, so I 
>> > decided to switch over to tap:aio for my file-backed domUs.  This isn't 
>> > working, either.  Whereas the domUs with file: at least boot and run, the 
>> > domUs with tap:aio: fail with this error:
>> >  
>> >   
> Hi Nick,
> we're running quite some Xen machines on SLES 10 SP1 here, too.
> I tried to switch from file:/ to tap:aio:/ (as xen documentation 
> recommends),
> without success. As far as I can see the creation itself works, but it locks
> down the machine shortly after accessing it.
> For now I do my testing on Dom0 (it's easier to see what's happening there).
> So here's what I tried:
> # Create 2 TB sparse file
> linux # dd if=/dev/zero of=/proj.stand/xen/disk2 bs=1M count=1 seek=2048000
> 1+0 records in
> 1+0 records out
> 1048576 bytes (1,0 MB) copied, 0,018314 seconds, 57,3 MB/s
> # Attach it to dom0 as /dev/hdb
> linux # xm block-attach 0 tap:aio:/proj.stand/xen/disk2 /dev/hdb  w 0
> linux # cat /proc/partitions
> ...
>    3    64 2097153024 hdb
> ...
> Now fdisk/mount this device - whatever you like.
> During my test the machine froze quite fast, however the same tests with 
> file:/
> work quite well - no idea why.
> Someone on the list, where this works?

Have you checked that the process "blktapctrl" is running on dom0 (ps ax
| grep blktapctrl)? If not, than your Kernel might be compiled without
blktap support. I'm using Xen with Debian-Etch in dom0 and the debian
xen-kernel has blktap-support disabled by default so I had to build a
custom kernel.

Gernot Kieseritzky

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