[linux-lvm] Why the dramatic increase in filesystem performance when usingxfs????
Gary.Mansell at ricardo.com
Fri Jan 21 10:51:09 UTC 2005
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.
# time dd if=/dev/zero of=./testfile bs=16384 count=250000 ; time sync
# 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
This e-mail and any files transmitted with it are confidential and intended
solely for the use of the individual or entity to whom they are addressed.
If you have received this e-mail in error please notify the sender immediately
and delete this e-mail from your system. Please note that any views or opinions
presented in this e-mail are solely those of the author and do not necessarily
represent those of Ricardo (save for reports and other documentation formally
approved and signed for release to the intended recipient). Only Directors
or Duly Authorised Officers are authorised to enter into legally binding
obligations on behalf of Ricardo unless the obligation is contained within
a Ricardo Purchase Order.
Ricardo may monitor outgoing and incoming e-mails and other telecommunications
on its e-mail and telecommunications systems. By replying to this e-mail you
give consent to such monitoring. The recipient should check this e-mail and
any attachments for the presence of viruses. Ricardo accepts no liability for
any damage caused by any virus transmitted by this e-mail. "Ricardo" means
Ricardo plc and its subsidiary companies.
Ricardo plc is a public limited company registered in England with registered
The registered office of Ricardo plc is Bridge Works, Shoreham-by Sea,
West Sussex, BN43 5FG.
More information about the linux-lvm