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Date:      Tue, 31 Jan 1995 14:45:58 -0800
From:      David Greenman <davidg@Root.COM>
To:        terry@cs.weber.edu (Terry Lambert)
Cc:        alan@picard.isocor.ie (Alan Byrne), questions@FreeBSD.org, alan@buster.internet-eireann.ie, mckusick@cs.berkeley.edu
Subject:   Re: disk optimization messages from kernel 
Message-ID:  <199501312246.OAA00250@corbin.Root.COM>
In-Reply-To: Your message of "Tue, 31 Jan 95 14:54:54 MST." <9501312154.AA28765@cs.weber.edu> 

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>> I've just recentlly upgraded to 2.0R.snap-190128. 
>> I upgraded due to problems with 1.1.5.1 + P90's with PCI cards (long story)
>> 
>> While I was installing the src distribution in /usr/src I got the 
>> following messages on the console, should I worry about them.
>> 
>> /usr: optimization changed from TIME to SPACE
>> /usr: optimization changed from SPACE to TIME
>> /usr: optimization changed from TIME to SPACE
>> /usr: optimization changed from SPACE to TIME
>
>UFS by default will time-optimize placement of blocks to speed read access.
>
>When the disk goes over a certain threshold, it switches from time to space
>optimization, on the theory that anything that works is better than anything
>that doesn't -- that is, it is better you don't run out of disk than you be
>able to read from it as fast as possible.
>
>When you drop back below the threshold, plus a watermark, it switches back.

   Actually, there is a bug in the 4.4 code that triggers the change almost
gratuitously when the filesystem is far from reaching the threshold. It then
flops back and forth a few times as more files are added. In other words, it's
quite broken and was added to my bugs-to-fix whiteboard about a month ago.

-DG



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