Xref: utzoo comp.unix.i386:2297 comp.unix.wizards:20144
Path: utzoo!utgpu!jarvis.csri.toronto.edu!clyde.concordia.ca!uunet!mcsun!ukc!dcl-cs!aber-cs!pcg
From: pcg@aber-cs.UUCP (Piercarlo Grandi)
Newsgroups: comp.unix.i386,comp.unix.wizards
Subject: Re: sadp on i386
Summary: sadp is not supported because of laziness and space
Keywords: sadp i386
Message-ID: <1583@aber-cs.UUCP>
Date: 12 Jan 90 18:29:20 GMT
Reply-To: pcg@cs.aber.ac.uk (Piercarlo Grandi)
Followup-To: comp.unix.wizards
Organization: Dept of CS, UCW Aberystwyth
	(Disclaimer: my statements are purely personal)
Lines: 31

In article <7088@cbnewsh.ATT.COM> dwc@cbnewsh.ATT.COM (Malaclypse the Elder) writes:
    
    i guess the problem is that as disk controllers got more
    intelligent, much of the statistics that were collected
    by the kernel couldn't be directly measured.  the result
    is the implementers chose not to provide any measurements.

No. Most discs out there use very simple controllers, and even
SCSI controllers could be profiled easily by using block
numbers.

The real reasons why sadp is not supported are, in order of
importance:

	1) most system administrators would not use it, because
	they are lazy or not competent enough.

	2) adding statiistics collection to a driver is an
	extra job to do; if the customer does not ask for it,
	it will be omitted.

	3) In some cases statistics collection requires a table
	whose size is combinatorial in the number of drives.

Point #3 is easy to obviate if statistics collection can be
disabled at system generation time. Points #1 and #3 are the
really important ones.
-- 
Piercarlo "Peter" Grandi           | ARPA: pcg%cs.aber.ac.uk@nsfnet-relay.ac.uk
Dept of CS, UCW Aberystwyth        | UUCP: ...!mcvax!ukc!aber-cs!pcg
Penglais, Aberystwyth SY23 3BZ, UK | INET: pcg@cs.aber.ac.uk