[dm-devel] persistent reservation behaviour with dm-multipath
Christophe Varoqui
christophe.varoqui at free.fr
Wed Jul 16 22:01:11 UTC 2008
The current dm-multipath behaviour is currently a potent data corrupter
on PR-based clusters sharing multipaths with the queue_if_no_path
feature on. Consider the following scenario :
- Node A take a write-exclusive persistent reservation on LU
- Node B submits a write io to LU, which is a sda-sdb multipath
- B dm_multipath routes the wio to sda, the wio is failed, the path is
marked failed
- B dm_multipath routes the wio to sdb, the wio is failed, the last
path is marked failed
- B queues the wio because of the queue_if_no_path feature. Process
submitting the wio is stuck in D-state.
- A releases the reservation. Queued wios are unqueued, corrupting the
data on LU.
I suspect wio returning a "reservation conflict" status should never be
queued.
DM suspend/resume on the multipath effectively flushes the queue, but
this solution leaves a window open for data corruption, between io
enqueue and user-space driven queue flush.
I saw Mike's Aug 2005 patches for scsi errors translation in block-layer
errors, which were a usable infrastructure to implement the desired
behaviour. Is some variant of this work headed for the upstream kernel ?
Regards,
cvaroqui
More information about the dm-devel
mailing list