Why would someone use JFS rather than raw disk access for a database application?
The real issue here is from a performance standpoint, do you want raw or filesystem access? JFS adds another layer to the I/O path. JFS is going to be slower than raw I/O. Yes, JFS has a log, but that is a log for the file system’s structure. The database would still need to be recovered after the fsck of JFS completed. With LVM, you can use raw I/O. A LV does not need to have a file system on it. So, you can do all the usual striping and mirroring with LVM and still have raw I/O (the database opens /dev/vgXX/rlvolX). However, there are many reasons customers use file systems. Namely, backup is a lot easier with file systems. Also, JFS’s online backup is great. Finally, many people like seeing their data (via bdf, etc).
