[linux-lvm] Why the dramatic increase in filesystem performance when usingxfs????

[Markus Baertschi]

If you browse through the extensive filesystem benchmarks at

http://fsbench.netnation.com/

You'll find results quite similar to yours. XFS is performing well for 
large sequential operations while ext3 without the writeback option can 
be half the speed.

I usually use ext3 for the OS volumes only, except with SuSE where 
reiser3 is the default. For other filesystems I prefer jfs for no 
exceptionally good reason but that I came to like it on AIX.

Markus


Gary Mansell wrote:
> Hi,
> 
> I have always run ext3 filesystem with journalling on Redhat AS as it is
> the only supported filesystem.
> 
> One of my colleagues runs xfs, though, and on comparable hardware
> configs he gets twice the performance compared to my ext3 tests.
> 
> The test that I perform is to create a file at least twice the size of
> the RAM installed in the system to avoid the possibility of cacheing,
> measuring the time to write and read the file back gives me the
> performance figure that I am after. I realise that this is a very simple
> test of large sequential IO but it is good enough for my needs.
> 
> ie
> 
> Write test:
> 
> # time dd if=/dev/zero of=./testfile bs=16384 count=250000 ; time sync
> 
> Read test:
> 
> # time dd if=./testfile of=/dev/null bs=16384
> 
> 
> As the xfs performance comes back about twice the performance of ext3
> for this test I am of the opinion that xfs must be cheating somehow. It
> has always been my opinion that the IO bottleneck is the hardware and
> not the filesystem hence changing the filesystem but using the same
> hardware should not make a huge difference to performance (you still
> have to get the same amount of data out to disk at the end of the day)
> 
> I am struggling to comprehend how xfs can cheat, though, as it can't
> cache such a huge file as there is not enough memory. Is it perhaps
> cheating because the file is comprised entirely of zero's?
> 
> Can someone please enlighten me
> 
> Thanks in advance
> 
> Gary Mansell


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