I'm setting up a couple of SL 5.1 file-servers and I'm wondering if I
can safely combine LVM snapshots with ext3 filesystems. I would like to
take a snapshot of my main user file system at midnight every night but
the question I have is "will the filesystem be in a consistent state?".
I'm concerned about in-memory caching of inodes, data, etc. happening at
the file-system level. 

Obviously, to safely snapshot a live file system the block-level device
needs to tell the file-system layer to sync to "disk" (i.e. disk and/or
block-level cache) and either temporarily suspend writes or just suspend
file-system cache changes. The LVM HOWTO says: "many of the filesystems
in the 2.6 kernel do this automatically when a snapshot is created" but
I can't find anything definite. If I can't do this then snapshotting
doesn't seem much different from just unplugging a disk!

Does anybody have any experience of this?

Thanks

John