Tagged queueing on Dell WS610 - good idea?

[P.C. Uiterlinden]

Neil,

The best way to find out is just to try it. Use bonnie to measure the throughput
with different queue depths. In stead of bonnie, you also could use dd to write
and read a large file. Make sure the file is large in either case (much larger
than your RAM).

Bonnie and dd gave comparable results in my case.

To my astonishment, it turned out that setting the queue depth larger than 2,
severely impacted throughput with my disks.

Below, I've pasted the results of bonnie. Notice that only write throughput
is affected.

Using two such disks in a RAID0 configuration doubles both read and write
throughput, but exhibits the same fall-off with queue depths of 3 or larger.

To make a long story short: just try it. As the saying goes: your mileage
may vary.

Regards,
Paul



aristoteles:~ # cat /proc/scsi/scsi
Attached devices:
Host: scsi0 Channel: 00 Id: 00 Lun: 00
  Vendor: SEAGATE  Model: ST34520W         Rev: 1444
  Type:   Direct-Access                    ANSI SCSI revision: 02
Host: scsi0 Channel: 00 Id: 01 Lun: 00
  Vendor: SEAGATE  Model: ST34520W         Rev: 1444
  Type:   Direct-Access                    ANSI SCSI revision: 02
Host: scsi0 Channel: 00 Id: 03 Lun: 00
  Vendor: HP       Model: HP35470A         Rev: T503
  Type:   Sequential-Access                ANSI SCSI revision: 02

Disk /dev/sdb: 255 heads, 63 sectors, 553 cylinders
Units = cylinders of 16065 * 512 bytes

   Device Boot    Start       End    Blocks   Id  System
/dev/sdb11          223       428   1654663   83  Linux native

              -------Sequential Output-------- ---Sequential Input-- --Random--
              -Per Char- --Block--- -Rewrite-- -Per Char- --Block--- --Seeks---
Machine    MB K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU  /sec %CPU
qdepth_1 1500 11009 74.8 11501 16.2  4167 12.0 11293 56.4 11671 10.8  50.1  0.8
qdepth_2 1500 10749 73.0 11257 16.1  3445  9.9 11139 56.7 11336 10.8  52.8  1.0
qdepth_3 1500  6596 44.3  7532 10.8  3252  9.3 10861 54.1 11502 11.4  56.0  1.1
qdepth_4 1500  6745 45.2  7380 10.6  3300  9.6 10899 54.5 11434 10.8  56.9  1.1
qdepth_8 1500  6909 46.4  7426 10.5  3237  9.5 10888 54.0 11368 11.4  57.2  1.2


Neil Conway wrote:
> 
> Hi - I've got RH6.0 on a bunch of Dell Workstations (mostly 610's).  By
> default, tagged command queueing isn't enabled on the RH kernel, and I'm
> wondering if it's safe and advisable to turn it on.  (I presume this
> would necessitate a reboot btw?).
> 
> Any tips will be gratefully received.
> 
> Config:
> Dell WS610 (2x550MHz Xeon, 1024MB RAM)
> On-board U2W (Adaptec AIC-7890/1 Ultra2)
> QUANTUM 9GB (ATLAS IV 9 WLS), and one of them has a QUANTUM 18GB 10k RPM
> (ATLAS 10K 18WLS).
> 
> Kernel 2.2.5 (RH's 2.2.5-15smp), and AIC7xxx driver 5.1.15/3.2.4
> 
> Thanks,
> Neil


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