On Sun, Feb 28, 2010 at 4:45 AM, Justin Piszcz [off-list ref] wrote:

On Sat, 27 Feb 2010, Bill Davidsen wrote:

quoted

Justin Piszcz wrote:

quoted

On Sun, 28 Feb 2010, Neil Brown wrote:

quoted

On Sat, 27 Feb 2010 08:47:48 -0500 (EST)
Justin Piszcz [off-list ref] wrote:

quoted

Hello,

I have two separate systems and with ext4 I cannot get speeds greater
than
~350MiB/s when using ext4 as the filesystem on top of a raid5 or raid0.
It appears to be a bug with ext4 (or its just that ext4 is slower for
this
test)?

Each system runs 2.6.33 x86_64.

Could be related to the recent implementation of IO barriers in md.
Can you try mounting your filesystem with
 -o barrier=0

and see how that changes the result.

NeilBrown

Hi Neil,

Thanks for the suggestion, it has been used here:
http://lkml.org/lkml/2010/2/27/66

Looks like an EXT4 issue as XFS does ~600MiB/s..?

Its strange though, on a single hard disk, I get approximately the same
speed for XFS and EXT4, but when it comes to scaling across multiple disks,
in RAID-0 or RAID-5 (tested), there is a performance problem as it hits a
performance problem at ~350MiB/s.  I tried multiple chunk sizes but
nothing
seemed to made a difference (whether 64KiB or 1024KiB), XFS performs at
500-600MiB/s no matter what and EXT4 does not exceed ~350MiB/s.

Is there anyone on any of the lists that gets > 350MiB/s on a mdadm/sw
raid
with EXT4?

A single raw disk, no partitions:
p63:~# dd if=/dev/zero of=/dev/sdm bs=1M count=10240
10240+0 records in
10240+0 records out
10737418240 bytes (11 GB) copied, 92.4249 s, 116 MB/s

I hate to say it, but I don't think this measures anything useful. When I
was doing similar things I got great variabilty in my results until I
learned about the fdatasync option so you measure the actual speed to the
destination and not the disk cache. After that my results were far slower
and reproducible.

fdatasync:
http://lkml.indiana.edu/hypermail/linux/kernel/1002.3/01507.html

How did you format the ext3 and ext4 filesystems?

Did you use mkfs.ext[34] -E stride and stripe-width accordingly?
AFAIK even older versions of mkfs.xfs will probe for this info but
older mkfs.ext[34] won't (though new versions of mkfs.ext[34] will,
using the Linux "topology" info).
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