On Sun, 24 Nov 1996 19:12:04 -0500 (EST) 
 Hacksaw <hacksaw@remote35.channel1.com> wrote:

 > the ccdconfig line:
 > # ccd           ileave  flags   compnent devices
 > ccd0            63      0       /dev/wd1e /dev/wd2e
 > 
 > So far so good. What should I use for the geometry of the ccd drive?

The ccd code will generate a pseudo-geometry for you.  Once you've done
ccdconfig, just "disklabel ccd0" ... it will print what the driver
calculated.

 > For that matter, is the interleave I chose even optimal?

I really should redo that section of the manual page.  It turns out
that you're a little better off simply maximizing the number of "large"
concurrent transfers, with the concurrency preferably happening
on multiple controllers.  Thus, if the ccd will be used for filesystem
activity, you should probably use (MAXBSIZE / DEV_BSIZE) for the
interleave.

So, a nice ccd would look sort of like this:

component	scsibus		target
0		0		0
1		1		0
2		2		0
3		3		0
4		0		1
5		1		1
6		2		1
7		3		1

...etc.  You get the idea :-)  If your interleave were (16k / DEV_BSIZE),
an optimal 64k transfer would happen concurrently across 4 SCSI busses.

Unfortunately, with IDE, you don't get _any_ concurrency.  Quite
honestly, with IDE, you'd be better off with pure concatenation
(interleave == 0).

Jason R. Thorpe                                       thorpej@nas.nasa.gov
NASA Ames Research Center                               Home: 408.866.1912
NAS: M/S 258-6                                          Work: 415.604.0935
Moffett Field, CA 94035                                Pager: 415.428.6939