On Dec 13, 2009, at 10:15 AM, Pasi Kärkkäinen <pasik at iki.fi> wrote: > 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." I wonder how long till it's backported to RHEL? -Ross