On Sun, Jan 04, 2009 at 03:02:37PM -0600, Roger Heflin wrote:
Yes, that is valid, so long as the md device is fairly quiet at
the time of the test. Since you already have a machine, please
post the mb type, and number/type of sata ports and the 1-disk,
2-disk, 3-disk,... numbers that you get.
I attached a little Perl script I hacked up for running many
instances of dd in parallel or individually. It takes one or more
block devices on the command line, and issues parallel dd reads for
each one. (Note my block size and count params are enormous; I made
these huge to avoid caching effects of having 4 GB of RAM.)
I have two MD arrays in my system:
$ cat /proc/mdstat
Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md1 : active raid5 sdb1[0] sdd1[3] sdc1[2] sde1[1]
2930279808 blocks level 5, 64k chunk, algorithm 2 [4/4] [UUUU]
md0 : active raid5 sdf1[0] sdi1[3] sdh1[2] sdg1[1]
2197715712 blocks level 5, 64k chunk, algorithm 2 [4/4] [UUUU]
unused devices: <none>
This is on Ubuntu server 8.04. Hardware is an Intel DQ35JO
motherboard (Q35/ICH9DO chipsets) with 4 GB RAM and an E5200 CPU.
- md1 has four WD RE2 GP 1 TB hard drives (the 5400 RPM ones).
These are drives are connected to two 2-port PCIe SATA add-on
cards with the Silicon Image 3132 controller.
- md0 has four WD 750 GB drives (neither "RE2" version nor
GreenPower). These drives are connected directly to the
on-board SATA ports (i.e. ICH9DO).
For md1 (RE2 GP drives on SiI 3132), it looks like I get about 80
MB/s when running dd on one drive:
$ sudo ./sata_performance.pl /dev/sd[b]
/dev/sdb: 13107200000 bytes (13 GB) copied, 163.757 s, 80.0 MB/s
With all four drives, it only drops to about 75 MB/s per drive:
$ sudo ./sata_performance.pl /dev/sd[bcde]
/dev/sdb: 13107200000 bytes (13 GB) copied, 171.647 s, 76.4 MB/s
/dev/sde: 13107200000 bytes (13 GB) copied, 172.052 s, 76.2 MB/s
/dev/sdd: 13107200000 bytes (13 GB) copied, 172.737 s, 75.9 MB/s
/dev/sdc: 13107200000 bytes (13 GB) copied, 172.777 s, 75.9 MB/s
For md0 (4x750 GB drives), performance is a little better; these
drives are definitely faster (7200 rpm vs 5400 rpm), and IIRC, the
SiI 3132 chipsets are known to be lousy performers.
Anyway, single drive performance is just shy of 100 MB/s:
$ sudo ./sata_performance.pl /dev/sd[f]
/dev/sdf: 13107200000 bytes (13 GB) copied, 133.099 s, 98.5 MB/s
And I lose virtually nothing when running all four disks at once:
$ sudo ./sata_performance.pl /dev/sd[fghi]
/dev/sdi: 13107200000 bytes (13 GB) copied, 130.632 s, 100 MB/s
/dev/sdf: 13107200000 bytes (13 GB) copied, 133.077 s, 98.5 MB/s
/dev/sdh: 13107200000 bytes (13 GB) copied, 133.411 s, 98.2 MB/s
/dev/sdg: 13107200000 bytes (13 GB) copied, 138.481 s, 94.6 MB/s
Read performance only drops a bit when reading from all eight
drives:
$ sudo ./sata_performance.pl /dev/sd[bcdefghi]
/dev/sdi: 13107200000 bytes (13 GB) copied, 133.086 s, 98.5 MB/s
/dev/sdf: 13107200000 bytes (13 GB) copied, 135.59 s, 96.7 MB/s
/dev/sdh: 13107200000 bytes (13 GB) copied, 135.86 s, 96.5 MB/s
/dev/sdg: 13107200000 bytes (13 GB) copied, 140.215 s, 93.5 MB/s
/dev/sdb: 13107200000 bytes (13 GB) copied, 182.402 s, 71.9 MB/s
/dev/sdc: 13107200000 bytes (13 GB) copied, 183.234 s, 71.5 MB/s
/dev/sdd: 13107200000 bytes (13 GB) copied, 189.025 s, 69.3 MB/s
/dev/sde: 13107200000 bytes (13 GB) copied, 189.517 s, 69.2 MB/s
Note: in all the above test runs, I actually ran them all three
times to catch any variance; all runs were consistent.
