Messages in this thread | | | Date | Sun, 28 Feb 2010 04:45:00 -0500 (EST) | From | Justin Piszcz <> | Subject | Re: mdadm software raid + ext4, capped at ~350MiB/s limitation/bug? |
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On Sat, 27 Feb 2010, Bill Davidsen wrote:
> Justin Piszcz wrote: >> >> >> On Sun, 28 Feb 2010, Neil Brown wrote: >> >>> On Sat, 27 Feb 2010 08:47:48 -0500 (EST) >>> Justin Piszcz <jpiszcz@lucidpixels.com> 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.
fdatasync: http://lkml.indiana.edu/hypermail/linux/kernel/1002.3/01507.html
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