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Date:      Wed, 27 Feb 2002 19:24:38 -0800 (PST)
From:      Doug Ambrisko <ambrisko@ambrisko.com>
To:        Terry Lambert <tlambert2@mindspring.com>
Cc:        Doug Ambrisko <ambrisko@ambrisko.com>, "Clark C . Evans" <cce@clarkevans.com>, freebsd-hackers@FreeBSD.org
Subject:   Re: read-only CD-ROM boot partition for vinum webfarm?
Message-ID:  <200202280324.g1S3Ocr60343@ambrisko.com>
In-Reply-To: <3C7D8106.28D8D2F4@mindspring.com>

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Terry Lambert writes:
| Doug Ambrisko wrote:
| > | The issue is that the MTBF for IDE CDROM drives is very
| > | low, comparatively, when they are forced to a continuous
| > | duty cycle.  This was discuseed two years ago, and I don't
| > | think the situation has improved any.  8-(.
| > 
| > Actually 2 years ago it got much better to be a non-issue.  4 years
| > ago with IDE CD-ROMs it was sketchy.  ... but what do I know being
| > responsible for manufacturing systems based on FreeBSD mounting root
| > via a CD-ROM in a dirty and hostile environment?
| 
| Hey, Doug!
| 
| I was basing my statement on the inability to use CDROMs
| for InterJets, which would have resolved the late-binding
| install issue for us.  8-).

That was not an issue.  Certain projects were exploring
this possibility as per my patches to boot FreeBSD CD-ROMs 
on IBM hardware.
 
| What's the MTBF for a CDROM being used as a swap backing
| store for program files and a root FS these days?

Enough, not to be an issue and probably on par to a typical hard
drive in practicle use.  I replaced 2 CD-ROMs and our manufacturer 
replaced atleast 2 IDE drives that I knew directly off.  Since 
they had a supply of hard drives I just had them deal with that.  
CPU fans and CPUs were more of an issue due to caked on dust in 
the machines.  Have to wonder how the dust effected the CD-ROM drives.
Fortunately at the time we used P5-133 that didn't need much 
cooling compared to todays CPUs so it was a while before they
failed.

Our manufacturing process definitely weeded out marginal drives
especially when we ran the "verify cd" command.  We used the 
hard disk only as a cache for the download images and /var all
binaries were run from the CD mounted as root which made login
in take long time.  You could hear the CD spin up and down
and seek all around.  The last time I had to be careful about
selecting a CD-ROM was when T-Zone was still in business!

Personally I don't care about MTBF, I care about how many times
I have to service something.  Since I tend to be lazy I try to 
use stuff that just works.  If the CD-ROMs weren't reliable
I don't think our entire manufacturing process would have 
depended on it.  BTW near the "end" we started running into a 
slew of hard drives that had a stiction problem and needed some 
help to get spinning again.  It was interesting to watch the
drives seeking with the drive apart, with me push starting the 
plater and asking people not to sneeze or cough on it while we
duplicated the disk to another drive.

Also we never had to worry about bad sectors or head slap before
hard disks were installed in system with a root mounted CD-ROM.  
This doesn't seem to appear in MTBF numbers.  Power outages
where not an issue or operators that power-cycled machines
as matter of process and we know that power outages can cause
bad sectors.

Now a cool thing would be to make a FreeBSD live CD that booted
up to multi-user for a quick demo.  With jhb's work this should
be a lot simpler to do now.  It would be the ultimate "fix-it" disk.

Doug A.

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