Theodore Tso wrote:
On Thu, Jul 10, 2008 at 08:36:42AM -0400, Ric Wheeler wrote:
Just to be mean, I have been trying to test the fsck speed of ext4 with
lots of small files. The test I ran uses fs_mark to fill a 1TB Seagate
drive with 45.6 million 20k files (distributed between 256
subdirectories).
Running on ext3, "fsck -f" takes about one hour.
Running on ext4, with uninit_bg, the same fsck is finished in a bit over
5 minutes - more than 10x faster. (Without uninit_bg, the fsck takes
about 10 minutes).
Is this too good to be true? Below is the fsck run itself, the tree is
Ted's latest git tree and his 1.41 WIP tools,
Wow. My guess is that flex_bg is making the difference. What we
would want to compare is the I/O read statistics line:
I/O read: 14198MB, write: 1MB, rate: 46.77MB/s
That's pretty good, and indicates we've avoided a *lot* of seeking.
The e2fsck -t -t output for ext3 should show roughly the same mount of
I/O read (with 20k files, there would be no advantage towards using
extents), but the I/O rate is probably *much* lower, indicating a lot
more seeking is going on.
We did run fsck through seekwatcher & saw a significant reduction in
seeks/sec for ext4. Eric has the pretty pictures that he can share.
Can you send the full e2fsck -t -t output of the ext3 run? And what
is the hdparm -t -t results of the disk?
I didn't run the ext3 test with -t -t (but can refill and rerun, takes
about 12 hours).
This disk is a relatively new Seagate 1TB drive, specs at:
http://www.seagate.com/ww/v/index.jsp?vgnextoid=0732f141e7f43110VgnVCM100000f5ee0a0aRCRD
hdparm test:
[root@localhost rwheeler]# /sbin/hdparm -t -t /dev/sdb
/dev/sdb:
Timing buffered disk reads: 186 MB in 3.03 seconds = 61.33 MB/sec
If I'm right, if you create the filesystem with mke2fs -t ext4dev -O
^flex_bg,^uninit_bg, you should see performance back to the old ext3
levels.
With uninit_bg off, it ran about 10 minutes, but it would be interesting
to run without either.
- Ted
P.S. We probably do want to examine the block allocation layout with
flex_bg to make sure that the filesystem ages well in the long term.
Testing aged file systems is always the holy grail - this workload is a
fairly artificial one and was laid down with 4 threads currently writing
to a shared subdirectory.
ric
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