Mike Snitzer wrote:

On 6/14/07, Paul Clements [off-list ref] wrote:

quoted

Mike Snitzer wrote:

quoted

Here are the steps to reproduce reliably on SLES10 SP1:
1) establish a raid1 mirror (md0) using one local member (sdc1) and
one remote member (nbd0)
2) power off the remote machine, whereby severing nbd0's connection
3) perform IO to the filesystem that is on the md0 device to enduce
the MD layer to mark the nbd device as "faulty"
4) cat /proc/mdstat hangs, sysrq trace was collected

That's working as designed. NBD works over TCP. You're going to have to
wait for TCP to time out before an error occurs. Until then I/O will 
hang.

With kernel.org 2.6.15.7 (uni-processor) I've not seen NBD hang in the
kernel like I am with RHEL5 and SLES10.  This hang (tcp timeout) is
indefinite oh RHEL5 and ~5min on SLES10.

Should/can I be playing with TCP timeout values?  Why was this not a
concern with kernel.org 2.6.15.7; I was able to "feel" the nbd
connection break immediately; no MD superblock update hangs, no
longwinded (or indefinite) TCP timeout.

I don't know. I've never seen nbd immediately start returning I/O 
errors. Perhaps something was different about the configuration?
If the other other machine rebooted quickly, for instance, you'd get a 
connection reset, which would kill the nbd connection.

--
Paul