Re: [Xen-API] XCP Storage resiliency

[George Shuklin <george.shuklin@xxxxxxxxx>]

I'm talking not about dom0, mostly, but domU kernel. If IO takes more 
than 120 seconds, it will processed as 'io timeout'.  And this timeout 
is hardcoded (no /sys|/proc variables).
If you getting IO timeout in less than 2 minutes - that different question.

19.06.2013 00:48, Nathan March ÐÐÑÐÑ:
> On 6/18/2013 1:08 PM, George Shuklin wrote:
> > AFAIK there is a hard timeout in linux kernels for stalled IO. 120 
> > seconds, if I remember correctly.
> > And there is no way to prevent those errors without playing with 
> > guest kernels and dom0 kernel.
> Strange thing is that things work beautifully on our xensource (using 
> blkback) but fail on xcp (using tap), so seems to be something 
> specific to tap that causes a failure to be returned to the VM has an 
> IO error. The VM's are identical between the two systems (including 
> kernel).
> I tried looking into adjusting the IO timeouts on the guest, but 
> unfortunately I don't have a timeout file in /sys/block/xvda/device/, 
> haven't tried tweaking things on the host side though.
> > 18.06.2013 03:47, Nathan March ÐÐÑÐÑ:
> > > Hi,
> > >
> > > Have been playing around with XCP and I'm looking to achieve high 
> > > resiliency in the situation of a backend NFS SR failure. I've got an 
> > > existing cluster based around xen open source and I've successfully 
> > > tested NFS outages of as long as 1 hour, during which IO/VMs simply 
> > > hang and upon recovery typically come back gracefully.
> > > Unfortunately when I try pulling access from an xcp host, it pretty 
> > > quickly (within a minute or two) starts returning I/O errors:
> > > [871449.552331] end_request: I/O error, dev tda, sector 26384232
> > > [871457.632417] end_request: I/O error, dev tda, sector 19276360
> > >
> > > Likewise in the VM I'm seeing I/O errors being returned:
> > >
> > > [ 4657.253261] end_request: I/O error, dev xvda, sector 19276432
> > > [ 4657.253264] Buffer I/O error on device xvda4, logical block 50002
> > > [ 4657.253268] lost page write due to I/O error on xvda4
> > > [ 4657.253275] end_request: I/O error, dev xvda, sector 19276440
> > > [ 4657.253283] end_request: I/O error, dev xvda, sector 19276448
> > >
> > > I've tried mounting the NFS SR with -o hard instead of the default 
> > > soft but it seemed to have no significant impact.
> > > Is what I'm looking to do possible with XCP? I'd simply like the vms 
> > > to hang while waiting for IO or optionally have the HV pause them (I 
> > > think vmware does this). Googling has failed me so any useful tips 
> > > would be appreciated, thanks!
> > > - Nathan
> > >
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> >
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