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From: rosso@sco.COM (Ross Oliver)
Newsgroups: comp.unix.xenix
Subject: Re: How is performance of ramdisk under SCO Xenix 2.2
Message-ID: <365@sco>
Date: Wed, 21-Oct-87 20:34:11 EDT
Article-I.D.: sco.365
Posted: Wed Oct 21 20:34:11 1987
Date-Received: Sat, 24-Oct-87 12:48:08 EDT
References: <522@drexel.UUCP> <4820@ncoast.UUCP>
Reply-To: rosso@sco.COM (Ross Oliver)
Organization: The Santa Cruz Operation, Inc.
Lines: 34

In article <4820@ncoast.UUCP> miket@ncoast.UUCP (Michael Taht) writes:
>In article <522@drexel.UUCP> jeff@drexel.UUCP (Jeff White) writes:
>>
>>  We just received our upgrade of SCO Xenix to version 2.2 today, and I
>>noticed in the manual that they now have a built in device driver for a 
>>ramdisk.  However, at the end of the manual page, they say that performance
>>can actually be WORSE, because the Xenix memory management can make better use
>>of the memory.
> ...
>In other words, the best way to get increased performance is Not To Use
>Xenix memory management! 
>I haven't even cracked my 2.2 doc.
>I believe, though, that a ramdisk emulating /usr/tmp and tmp would speed
>the performance of the C compiler greatly. (MSC, under Xenix is 7x slower
>than DOS). Does the Ram disk support multiple mount points, or do I 
>have to create several?


RAM disks are treated just like physical disks, so you would
need to create one RAM disk for each filesystem. However, the reason
for the warning in the doc is that XENIX already uses RAM buffers
to buffer disk I/O. When a disk block is "written" by a process,
it really goes into a RAM buffer to be written later. When a disk
block is requested, the kernel checks to see if it is already in
a buffer. If so, no access to the disk is needed. Therefore, for
all but a few specialized uses, RAM disks do not significantly
increase performance. Moreover, when a RAM disk is in use, there
is less memory available for user processes, so swapping is more
likely and will occur more often.

Ross Oliver
SCO Tech Support
{uunet, ucbvax!ucscc, decvax!microsoft}!sco!rosso
My opinions are my own, my employer denies my existence...