From: lampi@polari.online.com
Subject: Re: Third party disk drives on HP-UX
Summary: Come on in---the water's fine! :-)
Keywords: HP-UX disk drive 3rd third party
Organization: R Squared, Redmond, WA (206) 883-3116
Date: Fri, 4 Sep 1992 20:13:00 GMT

In article <trn.715289167@warper.jhuapl.edu> trn@warper.jhuapl.edu (Tony Nardo) writes:
>okuyama@pioneer.arc.nasa.gov (Darin Okuyama YR) writes:
>
>>Has anyone successfully installed a thrid-party SCSI disk
>>dirve on a Snake (HP 9000/700)?
>
>I installed a pair of disks from ADS (contained 2 Seagate ST41600N Elite
>drives, each with ~1.3 Gbytes storage).  So far they seem to work.
>
>

Being a third party, yes :-)

>>If you have, then:
>
>>  (1) Was it relatively straightforward?
>
>Moderately.  The hardest part was researching the drive's operating
>parameters (i.e. # of sectors, # of tracks, # of cylinders).  Beyond that,
>SAM gave me the info I needed to add support for the drive.  SAM will tell
>you which files to modify so that you may add a new "Disk drive model" to
>the system.
>
Very straightforward, but with one caveat (see below)

>>  (2) What problems did you encounter?
>
>I lost roughly 7% of the usable space on my disk due to the assumption by
>HP that all drives will have 1024-byte sectors.  They provide a workaround
>solution for those who have 512-byte sectors so that you may still use the
>drive.  However, a disk with an odd number of 512-byte tracks will lose one
>track under the workaround.
>
Make that 1 block (512 bytes).

>I did not have access to the rotational speed of my drive, but 3600 seemed to
>be a fairly common number.  I used that, and it worked.  Whether I guessed
>correctly or whether the HP driver no longer uses this information, I cannot
>say.
>
The value for rpm seems to be ignored.

>>  (3) What advice can you give the Net?
>
>1) Have your drive's documentation available to determine the # of tracks,
>   sectors, & cylinders.  If you don't have this documentation, but you have
>   a similar model drive on a Sun, you can obtain this information with the
>   "dkinfo" command.  Other flavors of Unix may offer similar ways to
>   inspect disk information on other systems.

This information is not really necessary. (see below)
>
>2) Obtain the rotational speed of the drive.  (I was willing to take a
>   chance on 3600, lacking the proper number, but this may not be a good
>   idea.)

This is not really necessary. (see below)
>
>3) Use SAM to add the disk drive.  The files you need to modify are well
>   documented, and SAM tells you which files you'll need to change.  (Those
>   files, BTW, are /usr/sam/lib/disk_aliases and /etc/disktab.
>
Or you can do it by hand & just modify /etc/disktab.

>Good luck!
>--
>Tony Nardo,		   INET: trn@warper.jhuapl.edu, trn@aplcomm.jhuapl.edu
> Johns Hopkins Univ./APL   UUCP: {backbone!}mimsy!aplcomm!trn

(Below)
I've just run through some 300+ benchmark runs with different disk drives
(total of 6 drives) and different disktab entries. Here are the results
(which I presented at a Hardware & Peripherals SIG session at InterWorks):

1. Optimal disk geometries have no obvious relation to the physical
   geometry of any given disk drive.
2. Different disk geometries for a given disk drive can cause that disk
   drive to perform as far as 50% slower than optimal on sequential I/O.
3. Different disk geometries for a given disk drive can cause that disk
   drive to have writes perform much faster, the same as, or much slower
   than reads during sequential I/O.
4. The values specified for rpm, sector size and number of cylinders (rm#,
   se# and nc#) are ignored, at least in 8.0x.
5. Selecting the best geometry for your application may require the
   running of a series of benchmarks on your system.

-- 
-----
+-+  Michael Lampi       lampi@polari.online.com
|R|  R Squared           16398 NE 85th St., Suite 101, Redmond, WA 98052
+-+                      (206) 883-3116       fax (206) 883-2676