logical volume, snapshot and db backup

Recently, I get the chance to review the usage of the snapshot of a file-system.

In Linux, only logical volume supports this feature. Btrfs is also documented to support this feature.
In AIX, JFS supports snapshot. (But there is no document mention this in Linux's implementation)
In Solaris, ZFS directly support this. (ZFS provide logical volume management, raid management etc). UFS also supports this.

Logical Volume Snapshots - shows information on this topic.

So, is it possible use the snapshot feature to back up a database ?
Yes, it is possible in limited condition.

Here is the reference
PostgreSQL 8.3.8 Documentation Chapter 24. Backup and Restore 24.2. File System Level Backup - list the pros and cons of this.

MySQL Volume Snapshot for Backup also shows the similar information on this topic.

In short, if you want to use this feature, all files must be in the same filesystem/logical volume.
And this may take a long time to complete the job.