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

[Marcel Ritter <Marcel.Ritter@xxxxxxxxxxxxxxxxxxxx>]

Hi again,

I finally found some time to have a deeper look into my 
tap:aio:/tap:qcow: troubles:
Once again how I tested things:

mkdir /proj.stand/mnt
dd if=/dev/zero of=/proj.stand/dummy bs=1M count=40960
xm block-attach 0 tap:aio:/proj.stand/dummy xvda w 0
fdisk /dev/xvda
# create 1 primary partition here
mkreisers /dev/xvda1
mount /dev/xvda1 /proj.stand/mnt
while true; do time dd if=/dev/zero of=/proj.stand/mnt/file bs=1M 
count=20480; done
...

This works quite well (as 'file:/proj.stand/dummy' worked before).

However if I replace the "disk image file" with a sparse file (which is
created quite fast, and saves lots of disk space for the moment)

dd if=/dev/zero of=/proj.stand/dummy bs=1M seek=40959 count=1

and run the same test, the process will hang just a few minutes later
(or maybe it's just getting so slow, that no progress can be observed,
I can't say for sure).

If also found this behaviour when using sparse qcow files:

qcow-create -r 20480 /proj.stand/image.qcow
xm block-attach 0 tap:qcow:/proj.stand/image.qcow xvda w 0
... <insert test above here> ...

works fine, but without "-r (reserve)" flag, it fails miserably:

qcow-create 20480 /proj.stand/image.qcow
xm block-attach 0 tap:qcow:/proj.stand/image.qcow xvda w 0
... <insert test above here> ...
.... < this takes hours ... or more? Never finished for me)

So this is (in short) what works (and what not):

type:      sparse:      works:
file:/             no               yes
file:/             yes             yes
tap:aio:/      no               yes
tap:aio:/      yes             no
tap:qcow:/   no              yes
tap:qcow:/   yes            no

So for me it looks like blktap (or some other component) gets into 
trouble when
sparse files are used...

Any idea what's the cause of that?

BTW: The system I'm currently testing on is SLES 10 SP2.

Bye,
  Marcel

--
----
Dipl.-Inf. Marcel Ritter
Linux/Novell
Regionales Rechenzentrum Erlangen
Tel: 09131 / 85-27808
E-Mail: Marcel.Ritter@xxxxxxxxxxxxxxxxxxxx
----
Unix _IS_ user friendly... It's just selective about who its friends are.



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