Question About Bus Speeds (and SCSI in general)

[Wendell Smith]

I am trying to tune a certain server and am having trouble getting my
head wrapped around the fundamentals of it's scsi disk/bus system.

The server in question is a Netfinity 7000 M10 with a ServeRAID 3H Raid
controller. 

Let me try to provide a little background to better place my confusion
in your heads...

OS: RedHat 9.0

Kernel: 2.4.20-20.9smp 

dmesg output:

scsi0 : IBM PCI ServeRAID 5.10.21  <ServeRAID 3H>
  Vendor: IBM       Model: SERVERAID         Rev: 1.00
  Type:   Direct-Access                      ANSI SCSI revision: 02
  Vendor: IBM       Model: SERVERAID         Rev: 1.00
  Type:   Direct-Access                      ANSI SCSI revision: 02
  Vendor: IBM       Model: SERVERAID         Rev: 1.00
  Type:   Processor                          ANSI SCSI revision: 02
  Vendor: IBM       Model: SAF-TE            Rev: 2
  Type:   Processor                          ANSI SCSI revision: 02
Attached scsi disk sda at scsi0, channel 0, id 0, lun 0
Attached scsi disk sdb at scsi0, channel 0, id 1, lun 0
SCSI device sda: 17772544 512-byte hdwr sectors (9100 MB)
Partition check:
 sda: sda1 sda2 sda3 sda4 < sda5 sda6 >
SCSI device sdb: 71686144 512-byte hdwr sectors (36703 MB)
 sdb: sdb1 sdb2
scsi1 : Adaptec AIC7XXX EISA/VLB/PCI SCSI HBA DRIVER, Rev 6.2.8
        <Adaptec aic7895 Ultra SCSI adapter>
        aic7895C: Ultra Wide Channel B, SCSI Id=7, 32/253 SCBs

scsi2 : Adaptec AIC7XXX EISA/VLB/PCI SCSI HBA DRIVER, Rev 6.2.8
        <Adaptec aic7895 Ultra SCSI adapter>
        aic7895C: Ultra Wide Channel A, SCSI Id=7, 32/253 SCBs


Is this saying that I have three SCSI busses?

I initially looked at /proc/scsi/aic7xxx/1 and /proc/scsi/aic7xxx/2 and
found that the bus speed for each had been set to 40 MB/sec. This set
off a flag in my head because I had set the ServerRAID controller to
Ultra 2 SCSI speed which should be 80 MB/sec. Right?

So if I have three SCSI busses, are they fully independent of each other
with respect to the bus speed settings? 

How does the aic7xxx bus speed get set? Does it matter to me in this
case?

Would I be better off utilizing the 2nd and 3rd SCSI bus with respect to
this server and it's disks? (Both disks are set to Raid level 0)

The reason behind this line of questioning is that when I execute:

hdparm -t /dev/sd[a-b] I get a results of around 28 MB/sec

I would expect more from a SCSI system set to run at Ultra 2 speeds. By
the way, both disks are Ultra 2 rated so I don't feel there is an issue
there.

Any help with these question would be greatly appreciated. Any
documentation that you can point me to (with respect to SCSI system
within the context of Linux) would also be greatly appreciated.

Regards,

Wendell Smith