Path: utzoo!mnetor!uunet!husc6!mailrus!ames!ll-xn!mit-eddie!bloom-beacon!athena.mit.edu!nessus
From: nessus@athena.mit.edu (Doug Alan)
Newsgroups: comp.unix.wizards
Subject: Cylinder boundaries in 4.3BSD
Message-ID: <8808@eddie.MIT.EDU>
Date: 13 Apr 88 02:48:35 GMT
Sender: uucp@eddie.MIT.EDU
Reply-To: nessus@athena.mit.edu (Doug Alan)
Organization: Kate Bush and Butthole Surfers Fandom Center
Lines: 40

I have just hooked up a brand new spiffy Maxtor XT-4380E (a 340
formatted Megabyte, 5.25-inch disk drive) to a VAXstation (running
4.3BSD), and plan on using it with a root partition (a), a swap
partition (b), and a partition for the rest of the disk (g).  I have
two options regarding partition tables.  Since the disk controller we
are using lets me set things so that the drive is reported to be
whatever I want it to be, one of my options is to tell the drive to
report itself as a very large RD53 or RD54 (standard DEC drives), and
this will work fine.  I won't lose any space on the disk, because the
partition tables for the RD53 and RD54 have the 'g' partition set to
go from the end of swap space to the end of the disk, wherever that
may be.  If I chose to do this, however, then the 'b' and 'g'
partitions will not start at the beginning of a cylinder, which is
important for the proper performance fine-tuning of a 4.3BSD file
system.  (Of course, I *will* create a disktab entry specially
tailored for the XT4380, so at least the number of sectors/track and
tracks/cylinder will be set correctly.)

My other option is to add a partition table to the kernal specifically
for this drive.  If I chose to do this, though, I will then need a
special kernal just to use the drive, and this has serious
ramifications on system maintainability.  For example, if I boot the
system from your joe random boot tape, I will not be able to access
this drive, because the kernal on it will claim "NO PARTITION TABLE
FOR DISK TYPE: XT43".

So my question is, how much performance will I lose if my partitions
don't begin on cylinder boundaries?  Is it worth the hassle of making
up a special boot tape, for example, so that I can begin my partitions
on cylinder boundaries, and thus not lose performance due to incorrect
fine-tuning?  Or is the performance-loss due to a partition beginning
in the wrong place negligable?  And I shouldn't hassle with special
nonstandard partition tables?

|>oug /\lan

P.S.  Maxtor has just come out with a new 5.25-inch drive, the
      XT-8760, that is 680 formatted megabytes and only costs $3100.
      That's only $4.55 per megabyte!  Maybe I'll hook one of those up
      too sometime soon.