On Mon, 25 Feb 2008 14:26:15 +0100 Anders Henke <anders.henke@xxxxxxxx> wrote: > Hi, > > I'm currently stuck between Kernel LVM and DRBD, as I'm using Kernel > 2.6.24.2 with DRBD 8.2.5 on top of an LVM2 device (LV). > > -LVM2/device mapper doesn't support write barriers > -DRBD uses blkdev_issue_flush() to flush its metadata to disk. > On a no-barrier-device, DRBD should receive EOPNOTSUPP, but > it really does receive an EIO. Promptly, DRBD gives the > error message "drbd0: local disk flush failed with status -5". > > The physical disk (in LVM speak) is a RAID1 on a 3ware 9650SE-2LP > controller; the driver 3w-9xxx supports barriers and after moving my D > RBD device from the LV to a single partition on the same RAID1, the > error messages from DRBD vanished. > > I've posted a lengty summary of my findings to > > http://lists.linbit.com/pipermail/drbd-user/2008-February/008665.html > > ... where Lars Ellenberg from DRBD basically responded in > > http://lists.linbit.com/pipermail/drbd-user/2008-February/008666.html > > ... that DRBD does catch the EOPNOTSUPP for blkdev_issue_flush and > BIO_RW_BARRIER, but the lvm implementation of blkdev_issue_flush in > 2.6.24.2 aparently does return EIO for blkdev_issue_flush. > > So simply the question: how should a top-layer driver check wether a lower > device does support barriers? md-raid does check this way differently than > e.g. XFS does, while DRBD also adds a third way to check this. > Or is this "merely" a bug in drivers/md/dm.c? > (cc dm-devel) I'd say it's a DM bug. Probably a hard-to-fix one though. -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
