On Fri, Dec 11, 2009 at 09:20:24AM +0800, Christopher Chan wrote: > Mark Caudill wrote: > > Christopher Chan wrote: > >> Morten Torstensen wrote: > >>> On 08.12.2009 13:34, Chan Chung Hang Christopher wrote: > >>>>> Speaking for me (on Linux systems) on top of LVM on top of md. On IRIX > >>>>> as it was intended. > >>>>> > >>>> That is a disaster combination for XFS even now. You mentioned some > >>>> pretty hefty hardware in your other post... > >>> If XFS doesn't play well with LVM, how can it even be an option? I > >>> couldn't live without LVM... > >>> > >> I meant it in the sense of data guarantee. XFS has a major history of > >> losing data unless used with hardware raid cards that have a bbu cache. > >> That changed when XFS got barrier support. > >> > >> However, anything on LVM be it ext3, ext4 or XFS that has barrier > >> support will not be able to use barriers because device-mapper does not > >> support barriers and therefore, if you use LVM, it better be on a > >> hardware raid array where the card has bbu cache. > > > > Wait, just to be clear, are you saying that all use of LVM is a bad idea > > unless on hardware RAID? That's bad it if it's true since it seems to me > > that most modern distros like to use LVM by default. Am I missing something? > > > > Yes, the Linux kernel has long been criticized for a fake > fsync/fsyncdata implementation. At the latest, since 2001. Unless you > had your hard drive caches turned off, you were at risk of losing data > no matter what you used: ext2, ext3, reiserfs, xfs, jfs, whether on lvm > or not. > > Write barriers were introduced to give data guarantees with hard drives > that have their write cache enabled. Unfortunately, not everything has > been given barrier support. LVM and JFS do not have write barrier support. > https://www.redhat.com/archives/dm-devel/2009-December/msg00079.html "Barriers are now supported by all the types of dm devices." -- Pasi