Wren VI format.dat query

[D. Mark Abrahams]

Apparently there are different possible ways to format SCSI disks such as
the Wren V and Wren VI.  Perhaps something to do with "logical sectoring"
vs. "hard sectoring" -- I'm unclear on this.

In any case, different vendors quoted me different formatted sizes (total
number of sectors in the `c' partition) for these disks, all under SunOS.
Quotes ranged from 600 to 622Mb for the Wren V and from 650 to 690Mb for
the Wren VI.  For the Wren V, the vendor who quoted 622Mb said, in effect,
"we have clever format.dat parameters which get a bit more space out of
the disk".  Another vendor said "the format.dat parameters are not
engraved in stone; you can choose your own".

- Are there indeed different ways to format these disks for SunOS?
- If yes, what are they, and what are the issues and tradeoffs? 
	(access speed vs. maximum space?)
- Where do I find out more?

I'm particularly interested in the Wren VI (on the SS1, if it matters) as
this is the disk I plan to purchase.  (The vendor choice was made on
overall price including hardware maintenance price, not claimed Mb).  Here
is the format.dat entry this vendor uses.

disk_type = "CDC WrenVI 94196-766" \
	: ctlr = MD21 : fmt_time = 3 \
	: trks_zone = 15 : asect = 6 \
	: ncyl = 1626 : acyl = 2 : pcyl = 1632 : nhead = 15 : nsect = 53 \
	: rpm = 3600 : bpt = 30170

This gives ncyl*head*nsect = 1626*15*53 = 1292670 sectors = "only" 646Mb.
Can this be improved?  If you are using a Wren VI, what is your format.dat
entry and how did you arrive at it?

Tips, pointers, references, and RTFMs are all welcome.  (Which FM, and
where?).  Please e-mail me.  I'll summarize if requested.  Thanks!

Mark Abrahams		dma at stat.berkeley.edu
Statistics		dma at ucbstat.bitnet
UC Berkeley		ucbvax!stat!dma