[CentOS] XFS and LVM2 (possibly in the scenario of snapshots)

Fri Dec 11 00:24:30 UTC 2009
Christopher Chan <christopher.chan at bradbury.edu.hk>

> No mention of barriers in the man page, I'm also getting confused. is 
> device mapper used for software raid - i.e. /dev/mdX?

Nope. Software raid is the md layer. Nothing to do with dm. Two separate 
layers although they share a bit of stuff.

> If so what are the implications of barriers and where are they turned on 
> / off?

Barriers allow one to ensure true fsync/fsyncdata when used with hard 
disks that have their write cache enabled. This is not talking about 
hard drives connected to hardware raid controllers which is a different 
ball game.

> Forgive me for potential off topic, but I too run xfs on lvm which uses 
> mapper.......risky??

IF you are not using hardware raid with bbu cache and of course, if you 
have disabled the write caches on the hard drives connected to the raid 
via the raid controller.