On 26 Feb 2002, Urs Thuermann wrote: > I tried creating a snapshot of a ext2 file system on a LV. I expected > a fsck on the snapshot device to give no errors, i.e. a consistent > file system. This is ok, as long as there is no (or little) load on > the file system when creating the snapshot. > > However, on a busy file system, the created snapshot has lots of > errors found by fsck. > > Is it this what the VFS lock patch is for? If so, why hasn't it been > integrated into the standard kernel? Has it flaws in it? Maybe > performance wise? It deadlocks for XFS on smp under heavy writeload. I use a writeable snapshot patch and replay the log afterwards. I think, the VFS patch has some principal problems. Creating a snapshot with the VFS-lock patch applied is more or less equivalent to unmounting the file system, creating the snapshot of the device and remounting the file system. That means that all ongoing write operations must be suspended until the filesystem is in a "clean" state. This can take some time. Up to 15 minutes from my observations and that is way too long. I think the right way is: use a jornaling file system, take a snapshot, make the snapshot writeable, replay the log, make the snapshot readonly and dump it to tape or whatever you want. No races, no deadlocks, no problems. Anselm --- Anselm Kruis Tel. +49 (0)89-356386-74 science + computing ag FAX +49 (0)89-356386-37 Ingolstädter Str. 22 mailto: A.Kruis@science-computing.de D-80807 München WWW: http://www.science-computing.de/ ********************************************************************** *** Wir freuen uns auf Ihren Besuch *** *** *** *** CeBIT 2002 *** *** 13.-20.03.2002, Messegelände Hannover, Halle 11, F 64 *** *** *** *** Automotive Circle International *** *** 18.-19.04.2002, Bad Nauheim *** *** *** *** VDI-Tagung: Berechnung und Simulation im Fahrzeugbau *** *** 01.-02.10.2002, Congress-Centrum Würzburg *** *** *** ********************************************************************** _______________________________________________ linux-lvm mailing list linux-lvm@sistina.com http://lists.sistina.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://www.sistina.com/lvm/Pages/howto.html
