On 06/17/2010 02:51 PM, aragonx@dcsnow.com wrote:

quoted

Actually, you have not said a word about which controllers you use (for
the drives).  Using the wrong controller can drain speed a lot.  As from
the kernel benchmarks it seems like neither RAM nor computing power are
the bottlenecks.

Some SATA-controllers handle "nearly parallel" writes to multiple drives
better than others.  SiI products for example have a noticeable drop-off
for each disk you add.  Pretty late Intels nearly show no impact of many
disks in parallel.  So maybe that could be the topic you should be
after.  (And maybe a lspci could help :)

Stefan

Hi Stefan,

Here is the output of lspci.  There are 5 disks on the ATI controller.
Four of them are part of the RAID.  The last disk is on the JMicron
controller which is a PCIE-1x card.  I can move one more disk to the
JMicron controller if you think that would help.  Or just purchase a new 4
port controller?

lspci|grep SATA
00:11.0 SATA controller: ATI Technologies Inc SB700/SB800 SATA Controller
[IDE mode]
02:00.0 SATA controller: JMicron Technologies, Inc. 20360/20363 Serial ATA
Controller (rev 03)

---
Will Y.

[IDE mode] is probably a bad idea...a bios setting will change that.

Mine shows this:

00:11.0 SATA controller: ATI Technologies Inc SB700/SB800 SATA 
Controller [AHCI mode]

And my results on similar test show this (3x500gb raid5), single disk 
shows this speed, so raid write speed breaks down to about 60-70% of 
single disk speed:
dd if=/dev/sdb of=/dev/null bs=1M count=2048
2048+0 records in
2048+0 records out
2147483648 bytes (2.1 GB) copied, 28.8118 s, 74.5 MB/s


dd if=/dev/zero of=zerofile bs=1M count=2048 conv=fdatasync,notrunc
2048+0 records in
2048+0 records out
2147483648 bytes (2.1 GB) copied, 36.6523 s, 58.6 MB/s

dd if=/dev/zero of=zerofile bs=1M count=6144 conv=fdatasync,notrunc
6144+0 records in
6144+0 records out
6442450944 bytes (6.4 GB) copied, 113.893 s, 56.6 MB/s

dd if=/dev/zero of=zerofile bs=1M count=16384 conv=fdatasync,notrunc
^C15006+0 records in
15006+0 records out
15734931456 bytes (16 GB) copied, 277.814 s, 56.6 MB/s

And this for reads:
dd if=zerofile of=/dev/null bs=1M count=6144 conv=fdatasync,notrunc
6144+0 records in
6144+0 records out
6442450944 bytes (6.4 GB) copied, 53.8029 s, 120 MB/s