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Re: [Xen-API] Snapshot causes disk errors and VM crashes

  • To: 'Mark Benson' <md.benson@xxxxxxxxx>
  • From: Thanos Makatos <thanos.makatos@xxxxxxxxxx>
  • Date: Mon, 24 Nov 2014 10:06:21 +0000
  • Accept-language: en-GB, en-US
  • Cc: "xen-api@xxxxxxxxxxxxx" <xen-api@xxxxxxxxxxxxx>
  • Delivery-date: Mon, 24 Nov 2014 10:06:46 +0000
  • List-id: User and development list for XCP and XAPI <xen-api.lists.xen.org>
  • Thread-index: AQHQBK1K4fiUQcRZpEaGn+rvv5VNlZxpUbCQgABJAACAABqHkIABJvgAgAAqj6D///LIgIAEmJpA
  • Thread-topic: [Xen-API] Snapshot causes disk errors and VM crashes

> Where should I look now? I am relatively new to Xen but am going to be
> admin for this system eventually so needo t know these things :)

Just check all system logs around that time for anything of potential interest. 
Also, you could try strace'ing tapdisk when taking a snapshot to see which 
function call returns EFAULT. Instrumenting this in the SM code 
(/opt/xensource/sm/blktap.py) would the best solution but you can always do 
this manually.

> I see lots of errors like the following:
> Nov 20 09:39:21 kalimantan tapdisk[1899]: ERROR: errno -14 at
> vhd_complete: /var/run/sr-mount/34ff5733-1e1d-dc84-137e-
> 95c849222ca4/2f6a71be-c1e7-4463-a77c-0d0e627745a3.vhd: op: 5, lsec:
> 33456128, secs: 8, nbytes: 4096, blk: 8168, blk_offset: 4294967295
> Which most certainly lead to the VM experiencing I/O errors. errno -14 is
> EFAULT (bad address) which is returned to tapdisk by some fairly low level
> function, possible some system call, unfortunately there isn't more
> information related to that.
> Can you check your logs for anything of interest around that time?

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