incredibly poor SCSI performance - why ?

From: Paul Barton-Davis (pbd@Op.Net)
Date: Tue Apr 04 2000 - 23:48:51 EST


I've tried a variety of methods to measure the i/o performance I can
get from 2 of my Ultra2 SCSI disks (Seagate Cheetah and a Quantum
Viking II). I am hard pressed to get better than 17MB/sec from the
Cheetah, and 10MB/sec from the Viking.

I am aware that expecting the "80MB/sec" rate is not realistic, but
these values seem absurdly low. I am trying to figure out why this
should be happening. I did tests on entire disk partitions (/dev/sda,
/dev/sdb) and on a newly created file in a newly created ext2
filesystem.

--p

Configuration:
        SuperMicro P6DBU mobo, w/Adaptec 7890 SCSI controller onboard
        dual PII-450
        Seagate Cheetah 4.5GB, 5.2ms 10000RPM
        Quantum Viking II 4.5GB, 7.5ms 10000RPM
        
/proc/scsi/scsi:

Attached devices:
Host: scsi0 Channel: 00 Id: 00 Lun: 00
  Vendor: SEAGATE Model: ST34502LW Rev: 0005
  Type: Direct-Access ANSI SCSI revision: 02
Host: scsi0 Channel: 00 Id: 01 Lun: 00
  Vendor: SONY Model: CD-ROM CDU-76S Rev: 1.1a
  Type: CD-ROM ANSI SCSI revision: 02
Host: scsi0 Channel: 00 Id: 02 Lun: 00
  Vendor: QUANTUM Model: VIKING II 4.5WLS Rev: 5520
  Type: Direct-Access ANSI SCSI revision: 02
Host: scsi0 Channel: 00 Id: 03 Lun: 00
  Vendor: YAMAHA Model: CRW4416S Rev: 1.0b
  Type: CD-ROM ANSI SCSI revision: 02
Host: scsi0 Channel: 00 Id: 05 Lun: 00
  Vendor: Seagate Model: STT8000N Rev: 3.22
  Type: Sequential-Access ANSI SCSI revision: 02

/proc/scsi/aic7xxx/0:

Adaptec AIC7xxx driver version: 5.2.0/3.2.4
Compile Options:
  TCQ Enabled By Default : Disabled
  AIC7XXX_PROC_STATS : Disabled
  AIC7XXX_RESET_DELAY : 5

Adapter Configuration:
           SCSI Adapter: Adaptec AIC-7890/1 Ultra2 SCSI host adapter
                           Ultra-2 LVD/SE Wide Controller at PCI 0/14/0
    PCI MMAPed I/O Base: 0xfebff000
 Adapter SEEPROM Config: SEEPROM found and used.
      Adaptec SCSI BIOS: Enabled
                    IRQ: 10
                   SCBs: Active 0, Max Active 2,
                         Allocated 31, HW 32, Page 255
             Interrupts: 3478
      BIOS Control Word: 0x10a6
   Adapter Control Word: 0x1c5a
   Extended Translation: Enabled
Disconnect Enable Flags: 0xffff
     Ultra Enable Flags: 0x0000
 Tag Queue Enable Flags: 0x0000
Ordered Queue Tag Flags: 0x0000
Default Tag Queue Depth: 8
    Tagged Queue By Device array for aic7xxx host instance 0:
      {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255}
    Actual queue depth per device for aic7xxx host instance 0:
      {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1}

Statistics:

(scsi0:0:0:0)
  Device using Wide/Sync transfers at 80.0 MByte/sec, offset 15
  Transinfo settings: current(10/15/1/0), goal(10/127/1/0), user(10/127/1/0)
  Total transfers 2485 (1558 reads and 927 writes)

(scsi0:0:1:0)
  Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15
  Transinfo settings: current(44/15/0/0), goal(10/127/0/0), user(10/127/1/0)
  Total transfers 0 (0 reads and 0 writes)

(scsi0:0:2:0)
  Device using Wide/Sync transfers at 80.0 MByte/sec, offset 31
  Transinfo settings: current(10/31/1/0), goal(10/127/1/0), user(10/127/1/0)
  Total transfers 852 (815 reads and 37 writes)

(scsi0:0:3:0)
  Device using Narrow/Sync transfers at 8.0 MByte/sec, offset 31
  Transinfo settings: current(30/31/0/0), goal(10/127/0/0), user(10/127/1/0)
  Total transfers 0 (0 reads and 0 writes)

(scsi0:0:5:0)
  Device using Narrow/Sync transfers at 10.0 MByte/sec, offset 15
  Transinfo settings: current(25/15/0/0), goal(10/127/0/0), user(10/127/1/0)
  Total transfers 0 (0 reads and 0 writes)

/proc/interrupts:

           CPU0 CPU1
  0: 27921 16251 IO-APIC-edge timer
  1: 2221 953 IO-APIC-edge keyboard
  2: 0 0 XT-PIC cascade
  4: 92 111 IO-APIC-edge serial
  5: 0 1 IO-APIC-edge CS4232
 10: 1740 1756 IO-APIC-level aic7xxx, RME Digi9652
 11: 0 0 IO-APIC-level Trident 4DWave PCI
 12: 382 3491 IO-APIC-edge PS/2 Mouse
 13: 1 0 XT-PIC fpu
 15: 59810 29798 IO-APIC-edge WaveFront - ICS2115/MIDI
NMI: 44107 44107
LOC: 44090 44089
ERR: 0

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