RAID / multiple concurrent drive access

[phreak at liquednet.net]

Hello all.  I hope that this list can help me with this problem I have.  I
have an AIC-7880 on board controller, and 2 Seagate UW 4.5 gig 10,000 RPM
cheetah drives.  Each drive sustains about 13MB/s sequential reads, and
under NT I configured them as a very fast stripe set, handling about
20MB/s.  I tried this in linux, and the combined throughput is still only
13MB/s, and I even tried starting 2 dd commands at once to read from the
drives, and the combined throughput is stil only 13MB/s.  This seems to
indicate that the AIC-7xxx driver is not making use of disconnect/reselect
and/or tagged command queueing.  I am running linux 2.2.12 and have those
options enabled.  I am running on a dual PII-233 system.  I will include a
printout of my /proc/scsi/aic7xxx/0 file at the end of this email.  Any
thoughs on why I am having this problem and how to fix it would be greatly
apreciated.  

Adaptec AIC7xxx driver version: 5.1.19/3.2.4
Compile Options:
  TCQ Enabled By Default : Enabled
  AIC7XXX_PROC_STATS     : Disabled
  AIC7XXX_RESET_DELAY    : 3
Adapter Configuration:
           SCSI Adapter: Adaptec AIC-7880 Ultra SCSI host adapter
                           Ultra Wide Controller
    PCI MMAPed I/O Base: 0xe1800000
 Adapter SEEPROM Config: SEEPROM found and used.
      Adaptec SCSI BIOS: Enabled
                    IRQ: 15
                   SCBs: Active 0, Max Active 16,
                         Allocated 30, HW 16, Page 255
             Interrupts: 120253
      BIOS Control Word: 0x10b6
   Adapter Control Word: 0x005e
   Extended Translation: Enabled
Disconnect Enable Flags: 0xfffb
     Ultra Enable Flags: 0x0003
 Tag Queue Enable Flags: 0x0003
Ordered Queue Tag Flags: 0x0003
Default Tag Queue Depth: 8
    Tagged Queue By Device array for aic7xxx host instance 0:
      {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0}
    Actual queue depth per device for aic7xxx host instance 0:
      {8,8,1,1,1,1,1,1,1,1,1,1,1,1,1,1}
Statistics:
(scsi0:0:0:0)
  Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8
  Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0)
  Total transfers 19973 (19973 reads and 0 writes)
(scsi0:0:1:0)
  Device using Narrow/Async transfers.
  Transinfo settings: current(12/0/0/0), goal(0/0/0/0), user(0/0/0/0)
  Total transfers 100791 (61659 reads and 39132 writes)





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