🚀 go-pugleaf

cyf@sequent.com (Cyrus Foughty) writes:

>I have heard two theories about one element that affects disk transfer
>rate. Help me disect these and find which is true and which is false.
>Of course I feel that there will be some cases where both are true and
>both are false. So, based on that I will tell you that I am dealing 
>with the HP97560 SCSI-2 disk drive.

>Theory 1: 

>A higher transfer rate will result when using the outer tracks. "outer"
>is defined here as "tracks that are the greatest distance from the 
>spindle". I.E., track numbering starting at zero.

>Theory 2:

>A higher transfer rate will result when using the inner tracks.
>"inner" is defined here as "tracks that are the closest to the
>spindle". I.E., track numbering starting at maximum track number and 
>decreasing.

>                       Stuff Deleted

Two months ago I didn't know about zones on disks that take advantage
of the greater circumference of the outer zones.  It not only increases
capacity of a disk but performance as well.  I was using a Seagate Elite
disk to measure SCSI bus performance and found that if I moved to a 
different but equivalent system, I often couldn't duplicate the best
performance I had achieve elsewhere.  I used

	 timex dd if=/dev/rdsk/c0t0d0s9 of=/dev/null bs=16384 count=1024

and got a bandwidth of about 2.7 MB/second but if I used slice 0, I 
would get about 3.6 MB/second.  Evidently, the way we assign slices,
s0 starts on the outer track and works in.  Slice 9 is in near the
hub.  When the performance seem to be slice-dependent, we went to the
trouble of reading the disk specification.  Seagate calls the technique
"Zone Bit Recording" and trademarks "ZBRtm". The disk is divided into
14 zone where the sectors per track range from 85 on the outside to
61 on the inside.  Zone frequency and bytes/track correspond similarily.

A Seagate document says "Variable Drive Serial Transfer Rate (26 MHz - 
36 MHz) is transparent to host due to buffered interface."  The 
variable transfer rate was not transparent in my test.  We may not 
have tuned the buffer interface.

I don't know about the HP97560, specifically, but I have heard that
some HP disks do something like this but with just three zones, of
76, 88, and 96 sectors per track.

Not a spokesperson for anyone.

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