Path: utzoo!mnetor!uunet!husc6!bu-cs!madd
From: madd@bu-cs.BU.EDU (Jim Frost)
Newsgroups: comp.sys.ibm.pc
Subject: Re: 20 Meg versus 40 Meg
Message-ID: <19754@bu-cs.BU.EDU>
Date: 7 Feb 88 19:34:17 GMT
References: <950@its63b.ed.ac.uk>
Reply-To: madd@bu-it.bu.edu (Jim Frost)
Followup-To: comp.sys.ibm.pc
Organization: Boston University Distributed Systems Group
Lines: 54

In article <950@its63b.ed.ac.uk> dougie@its63b.ed.ac.uk (Dougie Nisbet) writes:
>We are intending buying a PC clone with 40 Megabytes of disk space.
>Is it more sensible to buy 2 X 20 Meg, or 1 X 40 Meg drives? I have
>heard rumours that the 2X20's run faster than 1X40. Does anyone know if
>this is in fact the case? Any other reasons for/against would also be
>appreciated.

This is a hard question to answer, but here are some things that may
help you choose.

Speed.  2 20Mb drives can operate faster than 1 40Mb drive merely
because you can be splitting data between more platters/heads.  This
becomes a consideration if you use software to configure both drives
as a single logical drive.  Several software packages do this,
although I have only used Bow Systems VFeature.  Note that most 20Mb
drives are slower than 40Mb drives, so you may actually lose
performance if you use 20Mb disks and you'll probably loose
performance if you use each 20Mb disk as an independent logical drive
since it will be impossible to split data between the two drives for
faster access.

Configuration.  Both 40Mb and 2x20Mb systems would have to be divided
into 2 logical drives if you don't use a software package to overcome
the MS-DOS 32Mb logical drive size limitation.  This can have profound
affects on your software.  A single 40Mb disk is much more flexible,
though.  You could make one 32Mb logical drive for data and place all
programs on the 8Mb partition.  This would speed backups since you
need only back up the program partition when you add a new program.

Reliability.  One of two drives is more likely to fail than a single
drive.  Unless you're using software to make a large logical drive on
two separate physical drives, having two small drives means your
system will still have a drive while you repair/replace the failed
drive, while having only one will leave you out of luck.  It is
important to note that higher storage drives tend to be newer and use
more reliable technology, which means that it's less likely that one
40Mb drive is going to fail than one 20Mb drive.  This is not
universally true but it's a good rule of thumb.  Taking each of these
factors into consideration, it would seem that a larger disk would be
slightly more reliable than several smaller ones.  If you cannot risk
down time, having more than one drive might be a deciding factor since
your system will still be running even if one drive fails, although in
a crippled state.

Conclusion.  I would recommend a single 40Mb drive.  This tends to be
less expensive than 2 20Mb drives (although not much) and would leave
the controller open for an additional drive later should you need it.
It also will be less demanding on your power supply.  Each other
factor depends on the type of drive you order and your particular
needs, but in general larger drives are faster and more reliable than
smaller ones due to improvements in technology over time.

jim frost
madd@bu-it.bu.edu