scsi & ide disk speeds?
Hi,
I have two different computers with SCSI disks, both with IBM brand,
one an DDRS-39310D (10GB) and the other an IBM DNES-309170w (10GB)
using the same kernel driver version, AIC7XXX, rev. 6.2.4 and debian
stock kernels 2.4.18-686 and 2.4.18-686-smp, respectively. The second
box reports much lower speeds at boot-up, and the performance is also
lower for box2. This is unexpected since both the SCSI driver and the
disk is newer. Anyone have a good explanation?
Also compared to the box2 IDE disk (with DMA enabled), the speeds for the
SCSI disks are inferior:
Box2:
Sep 10 10:06:32 box2 kernel: hda: IBM-DTLA-305020, ATA DISK drive
hdparm -d 1 /dev/hda
/dev/hda:
Timing buffered disk reads: 64 MB in 3.29 seconds = 19.45 MB/sec
/dev/hda:
Timing buffered disk reads: 64 MB in 3.35 seconds = 19.10 MB/sec
However, with DMA off the speed is very low:
hdparm -d 0 /dev/hda
/dev/hda:
Timing buffered disk reads: 64 MB in 15.26 seconds = 4.19 MB/sec
I've always thought SCSI disks are faster than the IDE disks, but this
does not seem to be the case (at least for device reads). Anyone have
a good explanation, or am I missing something?
Best regards,
Svante
BTW: Is there a good place to put in the hdparm -d 1 /dev/hda
somewhere at the boot scripts? I've added it to the
/etc/init.d/bootmisc.sh script. It would be very nice to have this as
default without making any manual changes, but I assume there are
reasons why not.
Box1:
Sep 8 20:49:08 box1 kernel: scsi0 : Adaptec AIC7XXX EISA/VLB/PCI SCSI HBA DRIVER, Rev 6.2.4
Sep 8 20:49:08 box1 kernel: <Adaptec 2940 Ultra SCSI adapter>
Sep 8 20:49:08 box1 kernel: aic7880: Ultra Wide Channel A, SCSI Id=7, 16/253 SCBs
Sep 8 20:49:08 box1 kernel: Vendor: IBM Model: DDRS-39130D Rev: DC1B
Sep 8 20:49:08 box1 kernel: Type: Direct-Access ANSI SCSI revision: 02
Sep 8 20:49:08 box1 kernel: (scsi0:A:6): 40.000MB/s transfers (20.000MHz, offset 8, 16bit)
Sep 8 20:49:08 box1 kernel: scsi0:A:6:0: Tagged Queuing enabled. Depth 8
Sep 8 20:49:08 box1 kernel: Attached scsi disk sdc at scsi0, channel 0, id 6, lun 0
Sep 8 20:49:08 box1 kernel: SCSI device sdc: 17850000 512-byte hdwr sectors (9139 MB)
hdparm -t /dev/sdc
/dev/sdc:
Timing buffered disk reads: 64 MB in 5.57 seconds = 11.49 MB/sec
/dev/sdc:
Timing buffered disk reads: 64 MB in 5.12 seconds = 12.50 MB/sec
Box2:
Sep 10 10:51:01 box2 kernel: scsi0 : Adaptec AIC7XXX EISA/VLB/PCI SCSI HBA DRIVER, Rev 6.2.4
Sep 10 10:51:01 box2 kernel: <Adaptec aic7895 Ultra SCSI adapter>
Sep 10 10:51:01 box2 kernel: aic7895C: Ultra Wide Channel A, SCSI Id=7, 32/253 SCBs
Sep 10 10:51:01 box2 kernel: Vendor: IBM Model: DNES-309170W Rev: SA30
Sep 10 10:51:01 box2 kernel: Type: Direct-Access ANSI SCSI revision: 03
Sep 10 10:51:01 box2 kernel: (scsi0:A:6): 11.626MB/s transfers (5.813MHz, offset 8, 16bit)
Sep 10 10:51:01 box2 kernel: scsi0:A:6:0: Tagged Queuing enabled. Depth 8
Sep 10 10:51:01 box2 kernel: Attached scsi disk sda at scsi0, channel 0, id 6, lun 0
Sep 10 10:51:01 box2 kernel: SCSI device sda: 17916240 512-byte hdwr sectors (9173 MB)
hdparm -t /dev/sda
/dev/sda:
Timing buffered disk reads: 64 MB in 6.78 seconds = 9.44 MB/sec
/dev/sda:
Timing buffered disk reads: 64 MB in 6.74 seconds = 9.50 MB/sec
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