Further testing has shown that with the 2.4.18-231 kernel and xfs filesystem layered over LVM, the freeze/snapshot feature is unreliable. I have read about a VFS-lock kernel patch that has apparently been around for many months, maybe longer. Does anyone know if this has been incorporated into the official kernel, or into the -aa kernels that are the base for SuSE kernels? Regardless how do I report the below as a bug report in hopes that it gets fixed eventually. (I have also sent an e-mail to the XFS support list, so maybe it is pointless to do with SuSE as well??) And yes, I know XFS is considered experimental by SuSE, but I assume that feedback like this is what will eventually get it more reliable. ====> My simple tests I just tried doing some snapshots under a couple of different i/o loads, and I found them unreliable with simultaneous write activity. I was using the latest SuSE kernel 2.4.18-231 on a Uniprocessor AMD machine. The LVM Volume Group (VG) and XFS filesystem (/data) was created at install time via the standard SuSE 8.0 install GUI. For all cases I was using a simple script to invoke the snapshot process and I was attempting to create a 2.5 Gig snapshot volume: xfs_freeze -f /data lvcreate --snapshot -L 2500m --name Data_snap /dev/VG/Data xfs_freeze -u /data lvremove -f /dev/VG/Data_snap I was invoking the above script by hand, so there were several seconds minimum between each iteration. 1) With zero i/o, I did 10 snapshots with no lockups. 2) With read-only i/o, I also did 10 snapshots with no lockups. (i..e dd if=/data/largefile of=/dev/null bs=64k) 3) With read/write i/o, I had a lockup on my very first snapshot attempt. (i..e dd if=/data/largefile of=/data/junk bs=64k) The lockup occured on the lvcreate step. A kill -9 of the lvcreate process had no effect. Issuing a xfs_freeze -u /data from a different ssh login, cleared the lockup. The whole purpose of the xfs_freeze utility is to allow the snapshot process to be guaranteed of taking a valid snapshot. Taking a snapshot of a journalled filesytem in flight can occasionally capture a corrupted filesystem image. I have also read about a VFS-lock kernel feature/patch that may or may not be part of the SuSE kernel which guarantees that the filesystem is quiescent without the use of xfs_freeze. If this feature is present in SuSE kernels, the appropriate fix may simply be to turn xfs_freeze into a dummy function that simply echos "xfs_freeze is not required on SuSE kernels." ==== Greg Freemyer Internet Engineer Deployment and Integration Specialist Compaq ASE - Tru64 v4, v5 Compaq Master ASE - SAN Architect The Norcross Group www.NorcrossGroup.com

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If anyone cares:

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The script I was writing/executing to test this was on the xfs filesystem I was trying to snapshot.

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I'm not sure why this was causing a problem, but moving it to a different filesystem that is not part of LVM has made it work reliably.

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Probably the problem was a direct conflict between xfs_freeze and trying to run a script from the frozen filesystem.

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Greg

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Any LVM or XFS experts out there,

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I'm testing LVM snapshots under xfs for the first time.

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I'm using LVM from the SuSE 8.0 release and a updated SuSE kernel that was released at the end of July.

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k_deflt-2.4.18-231.i386.rpm

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I tried a simple lvcreate --snapshot -L 25m --name config_snap /dev/VG1/config lvscan lvremove /dev/VG1/config_snap

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and it worked fine. (I only tried it once.)