[Xen-users] Dell Poweredge 2650 - heavy IO hangs domU machines; xen 2.0.7, xen kernel 2.6.11.12

[Stephen Bosch <posting@xxxxxxxxxxx>]

Hello:

We are running three domU machines on a Dell 2650 and using Bacula to do
backups to an Exabyte VXA SCSI tape drive attached to the external
channel of a PERC 3 DC, with a RAID 1 running on the internal channel.

Xen version is 2.0.7
Kernel is xen-kernel-2.6.11.12

We have the bacula storage daemon running on dom0.

When we begin a large backup (several gigabytes), all of the domU
machines will lock up, regardless of whether they are involved in the
backup or not.

Characteristics of the lockup:
- We lose all network connectivity to all of them. We cannot ping or ssh
to them -- you cannot do anything. Even an nmap fails.

- the dom0 is still running fine.

- We can 'xm console' to the affected domU's and get a login prompt, but
we can only enter the login id; the login times out waiting for the
password prompt.


Eventually, the bacula backup will time out: at this point, the machines
come back to life. This takes about 15 - 20 minutes. The backup,
however, does not complete successfully. In fact, very little happens on
the backup at all :)

We're very puzzled by this -- we suspect an interrupt issue, but we
really don't have a clue where to start looking. Other people seem to
have reported similar IO-related problems.

Ideas?

-Stephen-

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