[Linux-cluster] GNBD & Network Outage
nigel.jewell at pixexcel.co.uk
Tue Jan 25 10:43:36 UTC 2005
We've been looking at the issues of using GNBD to provide access to a
block device on a secondary installation and we've hit a brick wall. I
was wondering if anyone had seen the same behaviour
On host "A" we do:
gnbd_export -d /dev/sda2 -e foo -c
On host "B" we do:
gnbd_import -i A
... and as you would expect /dev/gnbd/foo appears on B and is usable.
We have no other aspects of GFS in use.
Now - in order for this to be useful, we've been testing the effects of
using GNBD if there is a LAN outage. If we write a big file to a
mounted file system on B:/dev/gnbd/foo and pull out the LAN cable
halfway through the data being synced to A, host B never gives up trying
to contact A. In fact, if you plug in the cable 10 minutes later the
Now - on the surface - this doesn't seem like a big problem, but it is
when you try and use the imported device alongside software RAID or when
you want to do something "normal" like reboot the box. Rebooting just
stops when it trys to unmount the file systems.
We want to use B:/dev/gndb/foo alongside a local partition on B and
create a RAID-1 using mdadm. In the same scenario (where the LAN cable
is pulled), the md device on B completely stops all of the IO on the
machine because (presumably) the md software is trying to write to the
gnbd device ... which is forever trying to contact host A ... and of
course never gives up. It would be nice if it did give up and the md
software continued the md device in degraded mode.
So the question is this (got there in the end). Can anyone suggest a
solution and/or alternative/workaround? Is it possible to specify a
time-out for the GNBD import/export for when the LAN does die?
MSN: nigel.jewell at pixexcel.co.uk
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