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
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