Performance impact of mkfs.xfs vs mkfs.xfs -f

[Shrinand Javadekar]

Hi,

I have 23 disks formatted with XFS on a single server. The workload is
Openstack Swift. See this email from a few months ago about the
details:

http://oss.sgi.com/archives/xfs/2015-06/msg00108.html

I am observing some strange behavior and would like to get some
feedback about why this is happening.

I formatted the disks with xfs (mkfs.xfs) and deployed Openstack Swift
on it. Writing 100GB of data into Swift in batches of 20GB each gave
us the following throughput:

 20 GB: 93MB/s
 40 GB: 65MB/s
 60 GB: 52MB/s
 80 GB: 50MB/s
100 GB: 48MB/s

I then re-formatted the disks with mkfs.xfs -f and ran the experiment
again. This time I got the following throughput:

 20 GB: 118MB/s
 40 GB: 95MB/s
 60 GB: 74MB/s
 80 GB: 68MB/s
100 GB: 63MB/s

I've seen similar results twice.

Any ideas why this might be happening?

Thanks in advance.
-Shri