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SubjectRe: Limits of the 965 chipset & 3 PCI-e cards/southbridge? ~774MiB/s peak for read, ~650MiB/s peak for write?
On Sun, Jun 01, 2008 at 05:45:39AM -0400, Justin Piszcz wrote:

> I am testing some drives for someone and was curious to see how far one can
> push the disks/backplane to their theoretical limit.

This testing would indeed only suggest theoretical limits. In a
production environment, I think a person would be hard pressed to
reproduce these numbers.

> Does/has anyone done this with server intel board/would greater speeds be
> achievable?

Nope, but your post inspired me to give it a try. My setup is as
follows:

Kernel: linux 2.6.25.3-18 (Fedora 9)
Motherboard: Intel SE7520BD2-DDR2
SATA Controller: (2) 8 port 3Ware 9550SX
Disks (12) 750GB Seagate ST3750640NS

Disks sd[a-h] are plugged into the first 3Ware controller while
sd[i-l] are plugged into the second controller. Both 3Ware cards
are plugged onto PCIX 100 slots. The disks are being exported as
"single disk" and write caching has been disabled. The OS is
loaded on sd[a-d] (small 10GB partitions mirrored). For my first
test, I ran dd on a single disk:

dd if=/dev/sde of=/dev/null bs=1M

dstat -D sde

----total-cpu-usage---- --dsk/sde-- -net/total- ---paging-- ---system--
usr sys idl wai hiq siq| read writ| recv send| in out | int csw
0 7 53 40 0 0| 78M 0 | 526B 420B| 0 0 |1263 2559
0 8 53 38 0 0| 79M 0 | 574B 420B| 0 0 |1262 2529
0 7 54 39 0 0| 78M 0 | 390B 420B| 0 0 |1262 2576
0 7 54 39 0 0| 76M 0 | 284B 420B| 0 0 |1216 2450
0 8 54 38 0 0| 76M 0 | 376B 420B| 0 0 |1236 2489
0 9 54 36 0 0| 79M 0 | 397B 420B| 0 0 |1265 2537
0 9 54 37 0 0| 77M 0 | 344B 510B| 0 0 |1262 2872
0 8 54 38 0 0| 75M 0 | 637B 420B| 0 0 |1214 2992
0 8 53 38 0 0| 78M 0 | 422B 420B| 0 0 |1279 3179
And for a write:

dd if=/dev/zero of=/dev/sde bs=1M

dstat -D sde

----total-cpu-usage---- --dsk/sde-- -net/total- ---paging-- ---system--
usr sys idl wai hiq siq| read writ| recv send| in out | int csw
0 7 2 90 0 0| 0 73M| 637B 420B| 0 0 | 614 166
0 7 0 93 0 0| 0 73M| 344B 420B| 0 0 | 586 105
0 7 0 93 0 0| 0 75M| 344B 420B| 0 0 | 629 177
0 7 0 93 0 0| 0 74M| 344B 420B| 0 0 | 600 103
0 7 0 93 0 0| 0 73M| 875B 420B| 0 0 | 612 219
0 8 0 92 0 0| 0 68M| 595B 420B| 0 0 | 546 374
0 8 5 86 0 0| 0 76M| 132B 420B| 0 0 | 632 453
0 9 0 91 0 0| 0 74M| 799B 420B| 0 0 | 596 421
0 8 0 92 0 0| 0 74M| 693B 420B| 0 0 | 624 436

For my next test, I ran dd on 8 disks (sd[e-l]). These are
non-system disks (OS is installed on sd[a-d) and they are split
between the 3Ware controllers. Here are my results:

dd if=/dev/sd[e-l] of=/dev/null bs=1M

dstat

----total-cpu-usage---- -dsk/total- -net/total- ---paging-- ---system--
usr sys idl wai hiq siq| read writ| recv send| in out | int csw
0 91 0 0 1 8| 397M 0 | 811B 306B| 0 0 |6194 6654
0 91 0 0 1 7| 420M 0 | 158B 322B| 0 0 |6596 7097
1 91 0 0 1 8| 415M 0 | 324B 322B| 0 0 |6406 6839
1 91 0 0 1 8| 413M 0 | 316B 436B| 0 0 |6464 6941
0 90 0 0 2 8| 419M 0 | 66B 306B| 0 0 |6588 7121
1 91 0 0 2 7| 412M 0 | 461B 322B| 0 0 |6449 6916
0 91 0 0 1 7| 415M 0 | 665B 436B| 0 0 |6535 7044
0 92 0 0 1 7| 418M 0 | 299B 306B| 0 0 |6555 7028
0 90 0 0 1 8| 412M 0 | 192B 436B| 0 0 |6496 7014
And for write:

dd if=/dev/zero of=/dev/sd[e-l] bs=1M

dstat

----total-cpu-usage---- -dsk/total- -net/total- ---paging-- ---system--
usr sys idl wai hiq siq| read writ| recv send| in out | int csw
0 86 0 0 1 12| 0 399M| 370B 306B| 0 0 |3520 855
0 87 0 0 1 12| 0 407M| 310B 322B| 0 0 |3506 813
1 87 0 0 1 12| 0 413M| 218B 322B| 0 0 |3568 827
0 87 0 0 0 12| 0 425M| 278B 322B| 0 0 |3641 785
0 87 0 0 1 12| 0 430M| 310B 322B| 0 0 |3658 845
0 86 0 0 1 14| 0 421M| 218B 322B| 0 0 |3605 756
1 85 0 0 1 14| 0 417M| 627B 322B| 0 0 |3579 984
0 84 0 0 1 14| 0 420M| 224B 436B| 0 0 |3548 1006
0 86 0 0 1 13| 0 433M| 310B 306B| 0 0 |3679 836

It seems that I'm running into a wall around 420-430M. Assuming
the disks can push 75M, 8 disks should push 600M together. This
is obviously not the case. According to Intel's Tech
Specifications:

http://download.intel.com/support/motherboards/server/se7520bd2/sb/se7520bd2_server_board_tps_r23.pdf

I think the IO contention (in my case) is due to the PXH.

All and all, when it comes down to moving IO in reality, these
tests are pretty much useless in my opinion. Filesystem overhead
and other operations limit the amount of IO that can be serviced
by the PCI bus and/or the block devices (although it's interesting
to see if the theoretical speeds are possible).

For example, the box I used in the above example will be used as
a fibre channel target server. Below is a performance print out
of a running fibre target with the same hardware as tested above:

mayacli> show performance controller=fc1
read/sec write/sec IOPS
16k 844k 141
52k 548k 62
1m 344k 64
52k 132k 26
0 208k 27
12k 396k 42
168k 356k 64
32k 76k 16
952k 248k 124
860k 264k 132
1m 544k 165
1m 280k 166
900k 344k 105
340k 284k 60
1m 280k 125
1m 340k 138
764k 592k 118
1m 448k 127
2m 356k 276
2m 480k 174
2m 8m 144
540k 376k 89
324k 380k 77
4k 348k 71

This particular fibre target is providing storage to 8
initiators, 4 of which are busy IMAP mail servers. Granted this
isn't the busiest time of the year for us, but were not comming even
close to the numbers mentioned in the above example.

As always, corrections to my above bable are appreciated and
welcomed :-)

Bryan


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