[Xen-API] XCP Storage resiliency

[Nathan March <nathan@xxxxxx>]

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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