Re: EXT4 is ~2X as slow as XFS (593MB/s vs 304MB/s) for writes?
From: Eric Sandeen
Date: Mon Mar 01 2010 - 11:15:33 EST
Justin Piszcz wrote:
> On Sun, 28 Feb 2010, tytso@xxxxxxx wrote:
>> On Sat, Feb 27, 2010 at 06:36:37AM -0500, Justin Piszcz wrote:
>>> I still would like to know however, why 350MiB/s seems to be the maximum
>>> performance I can get from two different md raids (that easily do
>>> with XFS).
>> Can you run "filefrag -v <filename>" on the large file you created
>> using dd? Part of the problem may be the block allocator simply not
>> being well optimized super large writes. To be honest, that's not
>> something we've tried (at all) to optimize, mainly because for most
>> users of ext4 they're more interested in much more reasonable sized
>> files, and we only have so many hours in a day to hack on ext4. :-)
>> XFS in contrast has in the past had plenty of paying customers
>> interested in writing really large scientific data sets, so this is
>> something Irix *has* spent time optimizing.
> Yes, this is shown at the bottom of the e-mail both with -o data=ordered
> and data=writeback.
> === SHOW FILEFRAG OUTPUT (NOBARRIER,ORDERED)
> p63:/r1# filefrag -v /r1/bigfile Filesystem type is: ef53
> File size of /r1/bigfile is 10737418240 (2621440 blocks, blocksize 4096)
> ext logical physical expected length flags
> 0 0 34816 32768
> 1 32768 67584 30720
> 2 63488 100352 98303 32768
> 3 96256 133120 30720
> 4 126976 165888 163839 32768
> 5 159744 198656 30720
That looks pretty good.
I think Dave's suggesting of seeing what cpu usage looks like is a good one.
Running blktrace on xfs vs. ext4 could possibly also shed some light.
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