Dne 28.3.2012 20:26, Stuart D Gathman napsal(a): > Long ago, Nostradamus foresaw that on 03/28/2012 03:53 AM, Zdenek Kabelac > would write: >> It seems that your cfq scheduler should be tuned better for raid arrays - I >> assume you allow the system to create very large queues of buffers and your >> mdraid isn't fast enough to store dirty pages on disk - I'd probably suggest >> to significantly lower the maximum amount of dirty pages - as creation of >> snapshot requires fs sync operation it will need to wait till all buffers >> before the operation are in place. > A question (or minor nit): how could lvm possibly require a fs sync to create > a snapshot? I could see this for Xen, where guest OS has to support a com > channel to host. But for full virtualization, LVM doesn't know in general > what OS is running, or how to suggest an FS sync. Or is this something an > admin does, run a script that tells guest to sync before creating shapshot > through lvm (to maximize the amount of useful data in the snapshot)? You may check the man page for dmsetup suspend operation - options nolockfs and noflush. For lvm creation of snapshot I guess everyone wants to get the filesystem in 'stable' condition - so all in-flight operation before creation of snapshot happened should hit the disk - and if you run fsck you should get pretty consistent results. Or thin it would be preferable that flush & lockfs part should be skipped at this moment and users would get their snapshot fs in quite broken state ? zdenek _______________________________________________ linux-lvm mailing list linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
