Subject: Re: ccd performance
To: Dave Huang <>
From: Tom T. Thai <>
List: current-users
Date: 06/13/1997 18:17:17
Hmm.. the last time i read the man for ccd, it said that you CAN'T do 
stripping if the drives are not identical.  Am in incorrect or has this 

On Fri, 13 Jun 1997, Dave Huang wrote:

> I recently made my /usr a ccd (just for fun and 'cuz I think disk striping
> is nifty :) and was wondering how to determine the best interleave
> setting. Is the size of a track still a good guideline to use? My disks
> aren't identical--they're not even the same speed, which is probably
> especially evil.
> One's a 5400rpm Quantum Capella and the other's a 7200rp Quantum Atlas.
> Both are use ZBR (or whatever that thing's called where outer tracks have
> more sectors than the inner ones), but according to the messages when the
> drives are probed, one's got 126 sectors/track and the other's got 115. 
> I tried a ccd with an interleave of 127, and untarred the 600 megs of
> stuff that used to be on the drives before I made a ccd, and often there
> were rather lengthy periods (5s or more) where only one drive would be
> active. So, I reduced the interleave to 32 and did the untar again, and
> both drives seemed to run simultaneously more, although there were still
> some short periods where only one drive was active. I didn't actually try
> any benchmarks to see which way was better, but I figured that running
> both drives simultaneously was probably better :)
> On Fri, 13 Jun 1997, Jason Thorpe wrote:
> > If you find your freelist misses are high, you can set the kernel config
> > option "CCDNBUF" to some value.  That value indicates the number of
> > ccdbuf's that will be allocated per component.  The default is 8 (which,
> > in your case, means you have 2 components, since your hiwater is 16).
> Is "high" an absolute number (e.g. more than x is high), or relative
> compared to the number of ccdbuf allocations (e.g. over y% is high)?
> Name: Dave Huang     |   Mammal, mammal / their names are called /
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