Messages in this thread | | | Date | Tue, 5 Nov 2002 10:18:11 -0500 (EST) | From | Jim Lawson <> | Subject | [Q] How to flush disk cache w/read-only filesystem w/o unmount&remount? (shared SAN filesystem) |
| |
Greetings kernel-hackers -
I'm setting up a web farm with a number of Linux machines (ia32) attached via FC-AL to a shared SAN. There are 3 web servers, one of them mounts the filesystem read/write, the other 2 read/only. (Filesystem is currently ext3.)
Everything works "fine", until of course I try to modify files on the r/w server. Then we start seeing cache incoherency - the r/o systems now have "stale" information cached. Old versions of files and directories are not replaced.
I'm looking for a way to flush or invalidate the cache on the block device/filesystem, so that the system is forced to go all the way to the disk. Unmounting and remounting would accomplish this, of course, but that's tough to do in production.
This is a "read-mostly" application - I really only need to update the filesystem once a day or so - but I'd like to find a nice way to do it, without having to use NFS.
More info, if needed: Running Linux 2.4.18 (under Debian woody.) Using the qla2200 driver from Qlogic, although I don't think that matters - it looks like the caching happens in the VFS somewhere...
I've tried blockdev --flushbufs, which appears to do a BLKFLSBUF, but that seems to be equivalent to "sync" - just pushes the dirty buffers to disk, which doesn't help me.
Looking in fs/dcache.c, I see shrink_dcache_sb(struct super_block *), which *might* do what I want, but there doesn't seem to be any way to call that from user-land. And that probably just updates the dentries - I don't know if that has any effect on the file data.
Hoping someone with more kernel experience can enlighten me - Jim Lawson
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |