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From: Dmitry Monakhov <dmonakhov@openvz.org>
To: Justin Piszcz <jpiszcz@lucidpixels.com>
Cc: "linux-ext4\@vger.kernel.org" <linux-ext4@vger.kernel.org>,
       "linux-kernel\@vger.kernel.org" <linux-kernel@vger.kernel.org>,
       Alan Piszcz <ap@solarrain.com>
Subject: Re: EXT4 is ~2X as slow as XFS (593MB/s vs 304MB/s) for writes?
References: <alpine.DEB.2.00.1002261922010.8247@p34.internal.lan>
Date: Sat, 27 Feb 2010 03:46:39 +0300
In-Reply-To: <alpine.DEB.2.00.1002261922010.8247@p34.internal.lan> (Justin
	Piszcz's message of "Sat, 27 Feb 2010 03:31:02 +0300")
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Justin Piszcz <jpiszcz@lucidpixels.com> writes:

> Hello,
>
> Is it possible to 'optimize' ext4 so it is as fast as XFS for writes?
> I see about half the performance as XFS for sequential writes.
>
> I have checked the doc and tried several options, a few of which are shown
> below (I have also tried the commit/journal_async/etc options but none of 
> them get the write speeds anywhere near XFS)?
>
> Sure 'dd' is not a real benchmark, etc, etc, but with 10Gbps between 2 
> hosts I get 550MiB/s+ on reads from EXT4 but only 100-200MiB/s write.
>
> When it was XFS I used to get 400-600MiB/s for writes for the same RAID 
> volume.
>
> How do I 'speed' up ext4?  Is it possible?
I don't know how to speedup, but i do know how to slowdown XFS :)
Seems that you forget to call fsync at the end of file write
In this case some data may reside in memory cache.
Please add  "conv=fsync" or "conv=fdatasync" to the dd cmd.
And redone your measurements.
>
> raid0_11 disks: (XFS)
> # /dev/md0        /r1             xfs     noatime         0       1
> p63:/r1# dd if=/dev/zero of=bigfile1 bs=1M count=10240
> 10240+0 records in
> 10240+0 records out
> 10737418240 bytes (11 GB) copied, 18.1021 s, 593 MB/s
> p63:/r1#
>
> raid0_11 disks: (EXT4)
> # /dev/md0        /r1             ext4     noatime         0       1
> # dd if=/dev/zero of=file bs=1M count=10240
> 10240+0 records in
> 10240+0 records out
> 10737418240 bytes (11 GB) copied, 35.3741 s, 304 MB/s
> p63:/r1#
>
> Other tests (ext4)
> p63:~# mount /dev/md0 /r1 -o data=writeback
> p63:~# cd /r1
> p63:/r1# dd if=/dev/zero of=file bs=1M count=10240
> 10240+0 records in
> 10240+0 records out
> 10737418240 bytes (11 GB) copied, 39.8746 s, 269 MB/s
> p63:/r1#
>
> p63:~# mount /dev/md0 /r1 -o data=writeback,nobarrier
> p63:/r1# dd if=/dev/zero of=file bs=1M count=10240
> 10240+0 records in
> 10240+0 records out
> 10737418240 bytes (11 GB) copied, 40.0656 s, 268 MB/s
>
> Justin.
> --
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