On Mon, Feb 25, 2008 at 03:20:50PM -0800, Andrew Morton wrote: > On Mon, 25 Feb 2008 14:26:15 +0100 Anders Henke <anders.henke@xxxxxxxx> wrote: > > 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 That's right. > > -DRBD uses blkdev_issue_flush() to flush its metadata to disk. Which won't work if device-mapper is underneath. > > 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". > > I've posted a lengty summary of my findings to > > http://lists.linbit.com/pipermail/drbd-user/2008-February/008665.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. > I'd say it's a DM bug. The dm code is unchanged, but look at the limited endio handling in ll_rw_blk.c: static void bio_end_empty_barrier(struct bio *bio, int err) { if (err) clear_bit(BIO_UPTODATE, &bio->bi_flags); complete(bio->bi_private); } int blkdev_issue_flush(struct block_device *bdev, sector_t *error_sector) { ... wait_for_completion(&wait); if (error_sector) *error_sector = bio->bi_sector; ret = 0; if (!bio_flagged(bio, BIO_UPTODATE)) ret = -EIO; Alasdair -- agk@xxxxxxxxxx -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
