[ilug] Journaling filesystems -- Was : nuking /var and giving it to /usr

[Matthew French]

Conor Wynne wrote:
> I hear tell that the only LVM style journaling filesystem worth talking
> about it veritas VXFS, but it ain't free, as in beer.
> IBM's JFS is probably the next best apart from XFS which [apparantly] is
> more tailored to SGI's applications.

Erm, I think you are getting confused between volume managers and journaling
file systems?!? LVM is the "Logical Volume Manager".

A volume manager lets you dynamically resize partitions (if the file system
supports it). Very useful if you need to add another gigabyte to /var.

A journaling filesystem keeps track of changes to the filesystem, so that in
the event of a crash or power failure the file system is still in a
consistent state. Although files can still be lost, you won't - or rather
you should not - end up with unlinked i-nodes and incorrect file sizes.

> So for a database, what would you guys/gals recommend?

A very big: "It Depends".

Most transactional databases like Oracle and PostgreSQL are journaling
systems already - except that databases call the journal a transaction log.
:) Adding an extra journal at the filesystem layer gives no reliability
improvement.

For file based databases like Access and MySQL the journaling becomes more
useful. Unfortunately ReiserFS and ext3 will lose data if the system powers
off, and you may still have corrupt files. Again this depends on how the
database reads and writes data.

In both cases, journaling can alter performance, but it is difficult to say
if it makes the database faster or slower.

LVM adds nothing to reliability, but also has little impact on performance.
It could, however, save you many hours of administrative grief.

HTH,

- Matthew

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