Path: utzoo!mnetor!uunet!lll-winken!lll-tis!ames!hc!beta!unm-la!unmvax!turing.UNM.EDU!mike
From: mike@turing.UNM.EDU (Michael I. Bushnell)
Newsgroups: comp.unix.wizards
Subject: Re: How does filling a disk to capacity affect performance?
Message-ID: <954@unmvax.unm.edu>
Date: 15 Apr 88 05:38:23 GMT
References: <460@osupyr.mast.ohio-state.edu> <92@iravcl.ira.uka.de> <1508@se-sd.sandiego.NCR.COM> <182@aoa.UUCP>
Sender: news@unmvax.unm.edu
Reply-To: mike@turing.UNM.EDU.UUCP (Michael I. Bushnell)
Organization: University of New Mexico, Albuquerque
Lines: 28

In article <182@aoa.UUCP> mbr@aoa.UUCP (Mark Rosenthal) writes:

>Just a side note.  As I understand it, checking the return value of write()
>does not really tell you what you want to know, due to the fact that write's
>happen asynchronously.  All the return value can tell you is whether the data
>was successfully copied into the kernel's buffer.  Then when the disk is not
>busy and kernel gets around to it, the actual write happens, by which time your
>process is off doing other things, or perhaps has already exited.

Nope.  When your write returns, the only thing left to be done is
write the block to disk.  Specifically, the decision about which
hardware block to use, and the marking of the block used in the map,
has already been done.  No one else will get the block.  Once the
write returns, the write will finish without error (except for
possible hard errors).  Note that this guarantee is missing in NFS.
Sigh.




                N u m q u a m   G l o r i a   D e o 

			Michael I. Bushnell
			HASA - "A" division
14308 Skyline Rd NE				Computer Science Dept.
Albuquerque, NM  87123		OR		Farris Engineering Ctr.
	OR					University of New Mexico
mike@turing.unm.edu				Albuquerque, NM  87131
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