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Re: [dm-devel] [PATCH 1/6] dm raid45 target: export region hash functions and add a needed one

On Jul 10, 2009, at 11:23 AM, Heinz Mauelshagen wrote:

I extended dm-raid45's message interface to support changing the xor
algorithm and # of chunks, allowing for changes of the algorithm being
used at runtime.

Very useful indeed. I may send you some routines to be tested at some point in the future if you don't mind ;-)

This I used to perform a bunch of mkfs write intensive tests on the
Intel Core i7 system as an initial write load test case. The tests have
been run on 8 disks faked onto one SSD using LVM (~200MB sustained
writes throughput):

That's a little slower than I think you need for a good test. I'm not even sure I'm satisfied that my current SATA array is sufficient and I can get at least 500MB/s of write throughput to the disks using a raid0, possibly more if I can get a better eSATA port.

for a in xor_blocks
	for c in $(seq 2 6)
		echo -e "$a $c\n---------------"
		dmsetup message r5 0 xor $a $c
		for i in $(seq 6)do
			time mkfs -t ext3 /dev/mapper/r5
done > xor_blocks.out 2>&1

for a in xor_8 xor_16 xor_32 xor_64
	for c in $(seq 2 8)
		echo -e "$a $c\n---------------"
		dmsetup message r5 0 xor $a $c
		for i in $(seq 6)
			time mkfs -t ext3 /dev/mapper/r5
done > xor_8-64.out 2>&1

Mapping table for r5:
0 146800640 raid45 core 2 8192 nosync raid5_la 7 64 128 8 -1 10 nosync 1 8 -1 \ /dev/tst/raiddev_1 0 /dev/tst/raiddev_2 0 /dev/tst/raiddev_3 0 /dev/ tst/raiddev_4 0 \ /dev/tst/raiddev_5 0 /dev/tst/raiddev_6 0 /dev/tst/raiddev_7 0 /dev/ tst/raiddev_8 0

I attached filtered output files xor_blocks_1.txt and xor_8-64_1.txt,
which contain the time information for all the above algorithm/#chunks

Real time minima:

# egrep '^real' xor_blocks_1.txt|sort|head -1
real    0m14.508s
# egrep '^real' xor_8-64_1.txt|sort|head -1
real    0m14.430s

System time minima:

[root a4 dm-tests]# egrep '^sys' xor_blocks_1.txt|sort|head -1
sys     0m0.460s
# egrep '^sys' xor_8-64_1.txt|sort|head -1
sys     0m0.444s

User time is negligible.

This mkfs test case indicates better performance for certain dm-raid45
xor() settings vs. xor_blocks(). I can get to dbench etc. after my
vacation in week 31.

Thanks. This isn't too far off from what I would expect. I would say that real world loads fall all along a spectrum from "create lots of writes, but do little to no work" to "does lots of work, and only sporadically writes". It's the later end of this spectrum that is most likely to be helped by the cache avoiding routines, while the former is not. So, one of the tests I had in mind was to use something like timing a complete kernel build, or doing a database load/report cycle, or some other things like that. Things that do actual work in the foreground while the raid is kept busy in the background. Of course, testing all the various points along the spectrum is needed, so this test gets us the first.


Doug Ledford <dledford redhat com>


InfiniBand Specific RPMS

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