XFS and nobarriers on Intel SSD

[Richard Bade]

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)?

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.

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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