linux-ext4 - Re: Bad performance of ext4 with kernel 3.0.17

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Date:	Fri, 2 Mar 2012 08:50:55 +0800
From:	Xupeng Yun <xupeng@...eng.me>
To:	"Ted Ts'o" <tytso@....edu>
Cc:	Ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: Bad performance of ext4 with kernel 3.0.17

On Fri, Mar 2, 2012 at 03:47, Ted Ts'o <tytso@....edu> wrote:
> Two things I'd try:
>
> #1) If this is a freshly created file system, the kernel may be
> initializing the inode table in the background, and this could be
> interfering with your benchmark workload.  To address this, you can
> either (a) add the mount option noinititable, (b) add the mke2fs
> option "-E lazy_itable_init=0" --- but this will cause the mke2fs to
> take a lot longer, or (c) mount the file system and wait until
> "dumpe2fs /dev/md3 | tail" shows that the last block group has the
> ITABLE_ZEROED flag set.  For benchmarking purposes on a scratch
> workload, option (a) above is the fast thing to do.
>

Thank you Ted, I followed this and got the same result (read IOPS ~950
/ write IOPS ~100)

> #2) It could be that the file system is choosing blocks farther away
> from the beginning of the disk, which is slower, whereas the fio on
> the raw disk will use the blocks closest to the beginning of the disk,
> which are the fastest one.  You could try creating the file system so
> it is only 10GB, and then try running fio on that small, truncated
> file system, and see if that makes a difference.

I created LVM on top of the RAID10 device, and then created a smaller LV(20GB),
after that I took benchmarks against the very same LV with different
filesystems, the
results are interesting:

xfs (read IOPS ~1700 / write IOPS ~200)
ext4 (read IOPS ~950 / write IOPS ~100)
ext3( read IOPS ~900 / write IOPS ~100)
reisferfs (read IOPS ~930 / write IOPS ~100)
btrfs (read IOPS ~1200 / write IOPS ~120)

I got very bad performance from XFS
(http://www.spinics.net/lists/xfs/msg08688.html) about
two months ago, which was caused by known bugs of XFS, then I tried
ext4 on some of
my servers, it works very well until I got a new server set up with soft RAID10.

What should I learn to understand what's happening? any suggestion is
appreciated.

-- 
Xupeng Yun
http://about.me/xupeng
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