Re: Ceph + Xen - RBD io hang

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Hi James,

Can you post the contents of the hung task warning so we can see where it 
is stuck?

Thanks!
sage


On Tue, 27 Aug 2013, James Dingwall wrote:

> Hi,
> 
> I am doing some experimentation with Ceph and Xen (on the same host) and I'm
> experiencing some problems with the rbd device that I'm using as the block
> device.  My environment is:
> 
> 2 node Ceph 0.67.2 cluster, 4x OSD (btrfs) and 1x mon
> Xen 4.3.0
> Kernel 3.10.9
> 
> The domU I'm trying to build is from the Ubuntu 13.04 desktop release.  When I
> pass through the rbd (format 1 or 2) device as phy:/dev/rbd/rbd/ubuntu-test
> then the domU has no problems reading data from it, the test I ran was:
> 
> for i in $(seq 0 1023) ; do
>     dd if=/dev/xvda of=/dev/null bs=4k count=1024 skip=$(($i * 4))
> done
> 
> However writing data causes the domU to hang while while i is still in single
> figures but it doesn't seem consistent about the exact value.
> for i in $(seq 0 1023) ; do
>     dd of=/dev/xvda of=/dev/zero bs=4k count=1024 seek=$(($i * 4))
> done
> 
> eventually the kernel in the domU will print a hung task warning.  I have
> tried the domU as pv and hvm (with xen_platform_pci = 1 and 0) but have the
> same behaviour in both cases.  Once this state is triggered on the rbd device
> then any interaction with it in dom0 will result in the same hang.  I'm
> assuming that there is some unfavourable interaction between ceph/rbd and
> blkback but I haven't found anything in the dom0 logs so I would like to know
> if anyone has some suggestions about where to start trying to hunt this down.
> 
> Thanks,
> James
> _______________________________________________
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> ceph-users@xxxxxxxxxxxxxx
> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
> 
> 
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