[DRBD-user] Problems with drbdf on multipathed devices

Florian Haas florian.haas at linbit.com
Mon Oct 12 16:51:29 CEST 2009

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.

On 2009-10-12 15:51, Robert.Koeppl at knapp.com wrote:
> Hi all!
> I am experiencing some severe problems with drbd on multipathed devices.
> Setup consists of two Bladecenter H with HS21 Blades and Qlogic HBA,
> DS4700 Storages.
> Sles 11 x86_64, DRBD 6.3.4
> The system is running an oracle database and some custom made
> applications. As long as the nodes are connected to their respective
> storage systems, everyting works fine. If I disconnect the storage from
> the master node however, the drbd does not detach the drive, bit keeps
> happily running without reporting any error. The Kernel shows the paths
> and disks failed, so there seems to be a problem between the drbd and
> the devicemapper multipath drivers. Normal Path-failovers with only one
> path going down work well, so the dmmp seems to work ok.

This sounds like having no_path_retry set to "queue". At which point
dm-multipath will queue pending I/O indefinitely once all I/O paths
fail. In doing so, it will not pass any I/O errors to upper layers. And
so DRBD can never tell that there even is a problem.

> What I would need, is a system, that does fail over to the machine that
> still has physical connection to its disks.
> Handler is set to detach.

First, set no_path_retry to "fail" in your multipath.conf to ensure you
get I/O errors once both paths die.

Then, I'm not sure what you want. If you want just DRBD to fetch blocks
from the other node, then fine, go along with "detach". If you want the
entire system to fail over, then probably an "on-io-error
call-local-io-error", along with an local-io-error handler set to "halt
-f", is probably what you want to implement.


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