From: eletanjm@nuscc.nus.sg (TAN JIN MENG)
Newsgroups: comp.os.os2.misc
Subject: Re: Disk Performance Questions
Date: 28 Aug 92 02:21:57 GMT
Organization: National University of Singapore

hoppie@kub.nl (Jeroen Hoppenbrouwers) writes:
: After using OS/2 for a few weeks, and playing around with the settings
: in CONFIG.SYS, I'm bothered by some disk issues.
: 
: Long ago, while using plain DOS, I used 2 MB of disk cache using the
: Windows 3.1 version of SMARTDRV.EXE. This speeded up my 100 MB IDE disk
: to close to infinity. I loved it.
: 
: (Interludium: 486DX/33/256, 8MB, 100MB IDE, ET4000/1MB, 120MB tape, and
: some other toys)
: 
: When I switched over to OS/2 (will never switch back BTW) I first
: installed only a FAT system so I could easily flip back to DOS
: (games...). The default disk cache in CONFIG.SYS was 512 KB. I thought
: it was a bit small, but with only 8 MB RAM to spare I believed OS/2 needed
: the rest for itself. Lazy writes have always be ON.
: 
: Performance was a bit dissapointing. The disk really did a lot, and 
: clearly had to work factors harder than under DOS. I know perfectly well
: that OS/2 uses more small files instead of few larger ones, and swaps
: memory out to disk if necessary, but this was not what I expected.
: 

I had a HPFS file system. When I ran my DOS program in an emulated
session, its disk performance (read and writing a couple of MB) is very
close to disk performance under DOS with smartdrv.sys (90 to 95
percent).

: So I increased the disk cache to 2 MB, which I got used to under DOS.
: This improved the performance noticeably, but I still do not get the old
: DOS performance. I am only talking about disk access now. 

Increasing the disk cache size may or may not work - depending on your
working set. 1MB disk cache is probably enough (or more than enough).

: 
: As an experiment, I increased cache up to 4 MB but then OS/2 performance
: dropped severely :-) so I got back to 2 MB cache.
: 
3.5 MB for OS2 + 4 MB for cache  == A lot of swapping

: I defragment FAT disks every week, so this is not an issue.
: 
: 
: Questions:
: 
: 1 What is the typical cache setting for a FAT drive when you have 8 MB
:   physical RAM?

I'd suggest 384 to 512 KB as more suitable esp if you want to run more
than a couple of programs at a time.

: 
: 2 Will conversion to HPFS significantly increase raw performance? I know
:   about less fragmentation etc. but will I *feel* the difference?

Yes - I think so.

: 
: 3 It seems to me that OS/2 is just doing more than DOS, e.g. keeping
:   EA's and peeking all files while you open up a folder etc. This means
:   that raw disk performance will ever be less than DOS. Am I correct?
: 
Under HPFS, your EA's are kept together with the file instead of in a
separate file (as in FAT). Access to the EA + file is thus faster.

: 4 Is there a way to treat off disk space for speed, such as the (mmm) 
:   Windows Program Manager does, e.g. swallowing all icons instead of
:   reading them from disk every time? Should there be such a way?

Well if you keep the minimum of windows open at any one time - that may
help.

: 
: 5 Should I look to FAT disks under OS/2 as just a downward compatibility
:   tool or as a serious alternative to HPFS?
: 
Another feature of HPFS - more fault tolerence.

jin meng