[Openstack-operators] XFS documentation seems to conflict with recommendations in Swift

[Cole Crawford]

generally mounting with -o nobarrier is a bad idea (ext4 or xfs), unless you
have disks that do not have write caches. don't follow that

recommendation, or for example - fsync won't work which is something swift
relies upon.


On Thu, Oct 13, 2011 at 9:18 AM, Marcelo Martins
<btorch-os at zeroaccess.org>wrote:

> Hi Jonathan,
>
>
> I guess that will depend on how your storage nodes are configured (hardware
> wise).  The reason why it's recommended is because the storage drives are
> actually attached to a controller that has RiW cache enabled.
>
>
>
> Q. Should barriers be enabled with storage which has a persistent write
> cache?
> Many hardware RAID have a persistent write cache which preserves it across
> power failure, interface resets, system crashes, etc. Using write barriers
> in this instance is not recommended and will in fact lower performance.
> Therefore, it is recommended to turn off the barrier support and mount the
> filesystem with "nobarrier". But take care about the hard disk write cache,
> which should be off.
>
>
> Marcelo Martins
> Openstack-swift
> btorch-os at zeroaccess.org
>
> “Knowledge is the wings on which our aspirations take flight and soar. When
> it comes to surfing and life if you know what to do you can do it. If you
> desire anything become educated about it and succeed. “
>
>
>
>
> On Oct 12, 2011, at 10:08 AM, Jonathan Simms wrote:
>
> Hello all,
>
> I'm in the middle of a 120T Swift deployment, and I've had some
> concerns about the backing filesystem. I formatted everything with
> ext4 with 1024b inodes (for storing xattrs), but the process took so
> long that I'm now looking at XFS again. In particular, this concerns
> me http://xfs.org/index.php/XFS_FAQ#Write_barrier_support.
>
> In the swift documentation, it's recommended to mount the filesystems
> w/ 'nobarrier', but it would seem to me that this would leave the data
> open to corruption in the case of a crash. AFAIK, swift doesn't do
> checksumming (and checksum checking) of stored data (after it is
> written), which would mean that any data corruption would silently get
> passed back to the users.
>
> Now, I haven't had operational experience running XFS in production,
> I've mainly used ZFS, JFS, and ext{3,4}. Are there any recommendations
> for using XFS safely in production?
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