Subject: Re: Need Guidelines for Partitioning System Disk for a 48 MB System
From: Thomas Sippel - Dau <[email-masked]>
To: [email-masked]
Date: 27 Oct 92 19:56:39 GMT
Newsgroups: comp.sys.sgi

[email-masked] (Dale Atems) asks:
- A while back I posted a question asking what size swap partition I
- should use for a system with 48MB RAM. Nobody with any info responded,
- I assume because I prefaced the subject header with "FAQ". Judging from
- replies from people asking me to share whatever info I received in
- response, this is a Frequently Asked, but not a Frequently Answered,
- Question. :-)  So, I thought I'd try again...
- 
- Anyway, some more detail might be helpful: the system is an R3000
- Indigo and does not need to service large numbers of users at once.
- The reason for the RAM upgrade is to allow large (>16MB) processes to
- run without degrading performance on the graphics console. There is
- also only one hard disk drive (432MB), a floppy drive and a CD drive.

This is really difficult to answer in any concise way, as so much depends
on what you use the system for, and how you want the system to fail. The
options are:

    o   Graceful degradation: provide as much swap space as possible.
        If the machine gets too slow, users will turn away in disgust.

    o   High real time performance: provide as little as necessary, this
        forces virtually everything into real memory. The system will kill
        processes once they need more swap space than available.

There is, of course, a spectrum in between. Many processes contain large
chunks of text that is practically never used and there is no harm done if
that lot ends on disk rather than in real memory - error messages are a
case in point.

- Obviously with 48MB RAM, a swap partition of 40 Mbytes is too small to hold
- a system crash dump.

This is not a problem, as in case of crash the memory contents is dumped in
the /usr/adm/crash directory. It cannot be dumped on the swap space,
because under IRIX the swap space is added to the real memory to form a
pool of virtual memory. 

The only consideration I know of is that the system cannot be installed if
not enought swap space is on the system disk, as  the installation process
creates its root file system in the partition that will later be the swap
space.

In your particular situation, the answer is easy: leave the swap space at
40 Mbytes and monitor usage of real and virtual memory with:

       gr_osview -D file

where file contains for starters:
#--------------------------------------------start of file
#   gl applications specify bottom left corner
#   specifying an origin will select a default size which is too big
#
#   opt origin(4,700)            

#   specifying size means it is not resizeable
#   opt winsize(120,180)         

opt interval(5)
opt arbsize
cpu strip interval(8) samples(100) attack(0.5)
swp max tracksum(50)
rmem max tracksum(50)
wait tracksum
#--------------------------------------------end of file

Feel free to tune the file a bit more, see the man page for gr_osview.

You will find 4 bars, of which the second and third show swap space and
real memory usage. In your case, the second bar should be virtually empty
during the target usage. You will find that once some swap space has been
used, the usage will not drop below a certain minimum level, that is the
kind of junk I was talking about before.

Finally, you need more disk space, I usually recommend the rate:

                                    250 byte second
        disposable user filespace = ---------------
                                          flop

Disposable means that file space that users do not need to account for, it
excludes swap space, /tmp, /usr and whatever you have in sizeable
applications like explorer, khoros, avs, arc/info etc. It also excludes
whatever is in largish data files or packages that users can actually account
for, like "I need 300 Mbyte for developing X-windows improvements".

Thus for an R3000 Indigo (about 4 megaflops) you need 1 Gbyte in addition
to all the disk space already spoken for. I don't think this is enough for
multi-media development, but that would probably quickly be formalised and
fall under the "accounted for" space requirement.

Hope this helps a bit.                         Thomas

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