After watching Dave Chinner's talk on XFS at LCA, I decided to compare
it to ext4 on a small system.The small system I have handy today is my
Scientific Linux 6.1 desktop machine. Q660 Quad core processor. 4GB ram.
A single 1.5TB 7200rpm seagate SATA disk. 2.6.32-220.4.1.el6.x86_64
kernel, which Dave says has all the performance patches he covered in
his talk.

I put it into runlevel 3 and disabled all unnecessary services. Set up a
25GB logical volume formatted XFS. Mounted with Dave's suggested
options: inode64,logbsize=262144

I ran:

iozone -i0 -i1 -i2 -i4 -i8 -l 4 -u 4 -F 1 2 3 4 -s 2g

Which is 4 threads each working with a 2GB file, for a total of 8GB of
data.

I got the following throughput numbers:

59794 KB/s Write
60376 KB/s Rewrite
64557 KB/s Read
66706 KB/s Reread
----- Mixed Workload

I stopped the mixed workload test after 45 minutes. vmstat was reporting
about 700k/s in, 2k/s out. The drive light was on solid. Iozone was
using only a about 2% of processor. This seemed quite puzzling. Tried
again. Same result. Switching from CFQ to Deadline or Noop i/o scheduler
made no difference. No error messages in the log. And I was on a text
console, so would have seen any kernel messages immediately.

I reformatted to ext4 and mounted with default options. I got these
results:

68559 KB/s Write
60561 KB/s Rewrite
67697 KB/s Read
69353 KB/s Reread
----- Mixed workload

Better performance than XFS in the other tests. But same problem with
Mixed workload.

Obviously, the drive was getting seeked to death. (What else *could* it
be?)

So I ran:

iozone -i0 -i8 -l 1 -u 1 -F 1 -s 8g

which runs a single thread on 1 8GB file. Same problem.

I used this same iozone on a Scientific Linux 6.1 server running 3 drive
software RAID1 just a few days ago and got really nice numbers for all
tests, including mixed workload.

What in the world is going on here???

-Steve