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From: hotte@sunrise.in-berlin.de (Horst Laumer)
Newsgroups: comp.unix.internals
Subject: Re: What does sync() _really_ do?
Message-ID: <GBCMS9E@sunrise.in-berlin.de>
Date: 17 Dec 90 08:39:50 GMT
References: <CMM.0.88.661087867.steinar@fram.ifi.uio.no>
Organization: HL EDV-Beratung
Lines: 32

steinar@ifi.uio.no (Steinar Kj{rnsr|d) writes:


>The above subject and imposed question may seem trivial, but I have so far
>failed to find the answer (I browsed through the 4.3 book by McKusick, Karels
>and Quarterman, references to pertinent pages here are welcome). The question
>arised when a disk vendor presented results from a benchmark which purpose
>was to measure read/write transfer rates for his drive. His scenario
>was this:

> - a stand alone BSD (SunOS 4.0.3 I think) box in single user mode
> - no other disk activity in the system

>The test program looked something like this:

> - <write a HUUUUGE file and measure the write transfer rate>
> - sync(); sync(); sync();
> - <read the same file back again and measure the read transfer rate>
> 

As stated in the AT&T SysV Programmer, sync(2) is used to write memory
to disk *and* actualize the superblock. Thus, the succeeding read()
ought to find the file correctly, because the last blocks and superblock
where flushed to disk. sync(1/1M) is simply the same, but as stand-alone
binary.

--HL
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