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Date: Mon, 25 Feb 2008 14:26:15 +0100 From: Anders Henke <anders.henke@...d1.de> To: linux-kernel@...r.kernel.org Subject: device mapper not reporting no-barrier-support? 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? Anders -- 1&1 Internet AG System Architect Brauerstrasse 48 v://49.721.91374.50 D-76135 Karlsruhe f://49.721.91374.225 Amtsgericht Montabaur HRB 6484 Vorstand: Henning Ahlert, Ralph Dommermuth, Matthias Ehrlich, Andreas Gauger, Thomas Gottschlich, Matthias Greve, Robert Hoffmann, Markus Huhn, Achim Weiss Aufsichtsratsvorsitzender: Michael Scheeren -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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