On Tue, 6 Jun 2006, Andreas Dilger wrote:
On Jun 06, 2006 10:23 +0000, Holger Kiehl wrote:
Looking at ways to increase write performance on my system using ext3
Andreas Dilger pointed me to delalloc+mballoc+extent patches. Downloaded
those from ftp://ftp.clusterfs.com/pub/people/alex/2.6.16.8 and run some
benchmark, here some results using bonnie++:
[note: this is WITH extents,mballoc,delalloc enabled]
Version 1.03 ------Sequential Output------ --Sequential Input- --Random-
-Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP
2.6.16.19 16G 59223 91 264155 45 111459 36 57313 99 317944 63 1478 7
58814 92 276803 47 110418 36 57105 99 317534 65 1525 5
58299 92 274523 48 110290 36 56723 99 318839 65 1502 4
And here the results when mounting without extents,mballoc,delalloc option:
I was confused initially until I saw ^^^^^^^
Sorry for the confusion.
Version 1.03 ------Sequential Output------ --Sequential Input- --Random-
-Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP
2.6.16.19 16G 38621 98 194816 94 87776 49 37921 92 239128 54 1402 5
47000 99 194276 94 89232 49 38628 92 240539 55 1399 5
45873 98 178195 90 89726 50 38482 92 240490 55 1381 4
So using delalloc+mballoc+extent gives an approx. 30% increase in
performance.
Note also that there is a 50% reduction in CPU usage for writes (27% for
rewrites). This is important when you are trying to maximize IO from a
single server. I'm not sure why the read CPU usage increased, though it
may just be a result of increased memcpy due to the higher read throughput
(32% increase in read performance, 18% increase in CPU usage).
My main concern is write speed and here these patches help a lot. I have
not tested it, but I think this brings ext3 performance to that of ext2.
So the question is, why are these patches not included into the kernel?
I did some very extensive testing for several days and could not discover
any disadvantage using those patches. I must add that I did not test
crashes to see if data is lost. Are there any disadvantages using these
patches?
One of the main reasons this isn't in the kernel yet is that the extents
on-disk format is incompatible with the current ext3 on-disk format.
That is OK for Lustre because the storage servers are essentially
"appliances" that are used in well-controlled environments, but this
isn't so good when random users get involved. The patches couldn't be
merged until there was some consensus reached about the extents on-disk
format.
There is work currently underway with Red Hat, IBM, CFS, and Bull
to merge the extents support into the kernel.org ext3 code and the
official e2fsprogs, and this will likely also be in the upcoming RHEL5.
Once this is done it will be possible to merge the mballoc and delalloc
changes also.
Just to ensure that I understand this correctly. The on-disk format is not
final and it will still change. This means if I use it now I will have
to reformat the disk when ever the format is changed.
As you mention e2fsprogs also needs to be updated:
# dumpe2fs -h /dev/md7
dumpe2fs 1.38 (30-Jun-2005)
dumpe2fs: Filesystem has unsupported feature(s) while trying to open /dev/md7
Couldn't find valid filesystem superblock.
Are there any patches down loadable, that add support to the e2fsprogs?
It would really be nice if consensus about the extents on-disk format
could be reached, so more people could benefit from it. Asking when this
will be reached, does not make sense?
Thanks,
Holger
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