Tomasz Chmielewski, on 04/06/2009 02:29 PM wrote:
Bart Van Assche schrieb:
Hello Tomasz,
It would be great if you could publish the details of your setup and
the tests you have run, such that we are able to reproduce the tests
and analyze the results further.
Here it is.
The target is running Debian Lenny 64bit userspace on an Intel Celeron 2.93GHz CPU, 2 GB RAM.
Initiator is running Debian Etch 64 bit userspace, open-iscsi 2.0-869, Intel Xeon 3050/2.13GHz, 8 GB RAM.
Each test was repeated 6 times, "sync" was made and caches were dropped on both sides before each test was started.
dd parameters were like below, so 6.6 GB of data was read each time:
dd if=/dev/sdag of=/dev/null bs=64k count=100000
Data was read from two block devices:
- /dev/md0, which is RAID-1 on two ST31500341AS 1.5 TB drives
- encrypted dm-crypt device which is on top of /dev/md0
Encrypted device was created with the following additional options passed to cryptsetup
(it provides the most performance on systems where CPU is a bottleneck, but with decreased
security when compared to default options):
-c aes-ecb-plain -s 128
Generally, CPU on the target was a bottleneck, so I also tested the load on target.
md0, crypt columns - averages from dd
us, sy, id, wa - averages from vmstat
1. Disk speeds on the target
Raw performance: 102.17 MB/s
Raw performance (encrypted): 50.21 MB/s
2. Read-ahead on the initiator: 256 (default); md0, crypt - MB/s
md0 us sy id wa | crypt us sy id wa
STGT 50.63 4% 45% 18% 33% | 32.52 3% 62% 16% 19%
SCST (debug + no patches) 43.75 0% 26% 30% 44% | 42.05 0% 84% 1% 15%
SCST (fullperf + patches) 45.18 0% 25% 33% 42% | 44.12 0% 81% 2% 17%
3. Read-ahead on the initiator: 16384; md0, crypt - MB/s
md0 us sy id wa | crypt us sy id wa
STGT 56.43 3% 55% 2% 40% | 46.90 3% 90% 3% 4%
SCST (debug + no patches) 73.85 0% 58% 1% 41% | 42.70 0% 85% 0% 15%
SCST (fullperf + patches) 76.27 0% 63% 1% 36% | 42.52 0% 85% 0% 15%
Good! You proved that:
1. SCST is capable to work much better than STGT: 35% for md and 37% for
crypt considering maximum values.
2. Default read-ahead size isn't appropriate for remote data access
cases and should be increased. I slowly have been discussing it in past
few months with Wu Fengguang, the read-ahead maintainer.
Which IO scheduler on the target did you use? I guess, deadline? If so,
you should try with CFQ as well.
Thanks,
Vlad
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