Re: 2 IDE - 1 CD: which interfaces
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On Sunday 25 May 2003 3:00 pm, moseley@hank.org wrote:
> On Sun, May 25, 2003 at 09:13:50AM +0100, Alan Chandler wrote:
> > The answer depends on what you are using the disks for.
> >
> > Fundementally, for a given IDE channel, the two devices cannot be doing
> > IO at the same time. Because inherently the CD device is slower than a
> > disk (even if it can do dma) you are often advised not to put the two
> > together. However, if you hardly use the CD and could benefit from
> > overlaping operations between two hard drives (say one on hda and one on
> > hdc) then go ahead and do it.
>
> That's what I was wondering -- if just connecting the CD-ROM would effect
> the speed, or if it was only while the drive was operating. Didn't seem
> like just connecting the CD would slow down the entire interface.
I am pretty sure its only when IO is going on.
>
> So in my case where the CD is used, well, for just installing Debian and
> where I have my partitions on separate drives, it's better to place them as
> two masters and make the CD slave.
Exactly - think about where you want to put /var and /home - its just a guess,
but I expect those two get the most IO. Don't forget swap either - but only
if you don't have much memory and expect things to be swapping in and out.
>
> But if I'm, for example, ripping or burning CDs often then probably better
> to separate them. (in that case probably better to go with a SCSI cd-r...)
I recently blew up my scsi card driving my SCSI CD-R. It was cheaper in the
end to purchase a IDE CD-R than buy a new scsi card.
My setup now has disks on IDE 0 - as master and slave, and CD-R and DVD on IDE
1 (as master and slave). In my case the choice was not related to the IO
requirements but the length of the cables - with the DVD and CD sitting in
the 5 1/4 inch bays and the disks in the 3 1/2 inch it was impossible to link
disk and CD device on the same channel (I could JUST connect the top disk to
the bottom DVD - but that left the bottom disk and top CD-R unconnected).
>
> > that debian package sysstat contains iostat - which helps you see whats
> > going on.
>
> Thanks, that package has been on the back of my mind to install for months,
> if not longer.
>
> --
> Bill Moseley
> moseley@hank.org
- --
Alan Chandler
alan@chandlerfamily.org.uk
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