386GT Adaptec SCSI performance :-(

[neese at adaptex.UUCP]

>We recently put an ADAPTEC 1540A SCSI into a Compaq 386/20 as a second disk
>controller using 2.3.2GT.  The first contoller is the Compaq supplied WD1007.
>Performance on the SCSI disks are worse (I'm being kind) than were expected. 
>Here are some performance numbers all in kb/sec.:
>
>	disk		raw device	block device	large file
>
>	ESDI		340		319		288
>
>	SCSI		107		 57		 56
>
>The ESDI is a Compaq supplied 300mb Minisribe and the SCSI disks (2) are CDC
>Wren IV also 300mb.  The ESDI file system is fairly new and the SCSI file
>system is virgin.  BTW the correlation of block device to large file is worth
>noting in light of the benchmarks published here a week or so ago.
>
>I tried reformatting with adfmt but got an error.  Also the 1540A was jumpered
>for both sync and async negotiation with no change.
>
>Anybody have any ideas?

CDC by default ships the Wren IV drives with the read ahead buffer disabled.
If you enable this via the mode sense/select commands, then you will see
about a 400% increase in throughput.


			Roy Neese
			Adaptec Central Field Applications Engineer
			UUCP @ {merch,texbell,killer}!cpe!adaptex!neese