Re: XFS and nobarriers on Intel SSD

[Eric Sandeen <sandeen@sandeen.net>]

On 9/2/15 9:24 PM, Richard Bade wrote:
> Hi Everyone, I have a question about nobarriers. In the XFS FAQ it
> looks like the recommendation is that if you have a Battery Backed
> raid controller you should set nobarriers for performance reasons. 
> Our LSI card doesn’t have battery backed cache as it’s configured in
> HBA mode (IT) rather than Raid (IR). Our Intel s3710 SSD’s do have a
> capacitor backed cache though. So is it recommended that barriers are
> turned off as the drive has a safe cache (I am confident that the
> cache will write out to disk on power failure)?

If you have a device which guarantees that every acknowledged write
will persist even if power is lost, then you can safely turn off
barriers.

> The reason I am asking about this is that we are seeing some
> significant I/O delays on the disks causing a “SCSI Task Abort” from
> the OS. This seems to be triggered by the drive receiving a
> “Synchronize cache command”. My current thinking is that setting no
> barriers will stop the drive receiving a sync command and therefore
> stop the I/O delay associated with it.

Interesting, I thought that usually devices with battery-backed cache
will just ignore synchronize cache commands.
 
But if not, then sure, maybe that's the issue.

-Eric

> This is happening on our Ceph storage cluster. For those not familiar
> with Ceph, it uses XFS as the underlying filesystem for the object
> stores.
> 
> Has anyone else encountered this issue? Any info or suggestions about
> this would be appreciated.
> 
> Regards, Richard
> 
> 
> 
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