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From: John Nielsen <lists@jnielsen.net>
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Subject: recovering from or increasing timeouts on virtio block device
Date: Mon, 17 Feb 2014 13:21:19 -0700
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Cc: Bryan Venteicher <bryanv@freebsd.org>
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I run several FreeBSD virtual machines in a Linux KVM environment with a =
SAN. The VMs use virtio block storage, and the KVM hosts map the virtual =
volumes to targets on the SAN. Occasionally, failover or other =
maintenance events on the SAN cause it to be unavailable for 30+ =
seconds. When this happens, the FreeBSD VMs have hard failures on the =
vtbd* devices, and thereafter any attempted reads or writes return =
immediately with an error (even after the SAN is responsive again). The =
only way to recover a VM once that happens is to hard boot it.

Is there any way to adjust the timeouts or enable some kind of retry for =
the virtio block devices? It would be nice to be able to recover =
gracefully after a SAN event without needing to reboot the VMs.

Thanks!

John Nielsen