Justin Piszcz wrote:
On Sun, 28 Feb 2010, Neil Brown wrote:
On Sat, 27 Feb 2010 08:47:48 -0500 (EST)
Justin Piszcz <jpiszcz@xxxxxxxxxxxxxxx> wrote:
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.
--
Bill Davidsen <davidsen@xxxxxxx>
"We can't solve today's problems by using the same thinking we
used in creating them." - Einstein
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