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From: wehr@fmsrl7.UUCP (Bruce Wehr )
Newsgroups: comp.sys.hp
Subject: What are good disktab entries for the new HP670H disk drive?
Message-ID: <39465@fmsrl7.UUCP>
Date: 4 Apr 91 17:11:01 GMT
Organization: Ford Motor Company, Scientific Research Labs, Daerborn, MI
Lines: 57

Howdy,

We've got one of HP's new Series 6000 Model 670H disk drives. This is a
670Mb drive with the following geometry:

     256 bytes/sector
     113 sectors/track
      16 tracks/cylinder
    1449 cylinders

Since this is a new disk, there is no entry in /etc/disktab. No
problem, I'll roll my own. But the utilities that use disktab want to
talk about 1Kb sectors, not 256 byte sectors. So I sacrificed one 256
byte sector per track, claiming I've got 28 1Kb sectors/track. It
works, but it also works out to be nearly 6Mb being tossed out the
window (which I'd rather not do if I don't have to).

Here's an excerpt from /etc/disktab that talks about "fudging" disktab
numbers to solve a similar problem (ns#X represents the number of
sectors/track):

    #       ns#X  must be in multiples of 1k.  We must sometimes     #
    #       then "fudge" the numbers.  Example: A gray microfloppy   #
    #       formatted with format option 2 has this geometry:        #
    #          - 512 bytes/sector                                    #
    #          -   9 sectors/track                                   #
    #          -  77 tracks/surface                                  #
    #          -   2 surfaces                                        #
    #                                                                #
    #       We have to fool option 2, instead of 9 sectors of 512    #
    #       bytes with 2 heads, we specified 9 sectors of 1K with    #
    #       1 head (ns# REQUIRES 1K).                                #

This example look pretty clean. I'm sure I could come up with some
numbers that work out to represent the whole disk, but it wouldn't be
as clean as the example. It would probably work - but, I'm afraid I'd
kill disk performance.

Finally, the question: do I need to sacrifice 1% of my disk in the name
of performance (which I'm more than willing to do)? Or is there
something else I can do to use the entire disk without sacrificing
performance?

Any and all advice is appreciated (except RTFMs - I've done that).

As a second, minor question: /etc/disktab refers several times to a
'cs80describe' utility - I have no such beast. What's up? I think I saw
this question go by a while ago - and I didn't pay attention to the
responses.  Deserving flames tolerated - as long as they're accompanied
by useful information.

Thanks.
-- 
               Bruce Wehr (wehr%dptc.decnet@srlvx0.srl.ford.com)
                (..!uunet!srlvx0.srl.ford.com!wehr%dptc.decnet)
              Ford Motor Company - Engineering Technology Services
     P.O. Box 2053, Room 1153, Dearborn, Michigan 48121-2053 (313)337-5304