Re: Enquiry regarding Linux in Mission Critical situation

From: Robert Redelmeier (
Date: 06/28/02

From: (Robert Redelmeier)
Date: Fri, 28 Jun 2002 14:53:04 GMT

[fup2 comp.os.linux.advocacy] *** <> wrote:
: I am posting this information to find out the true extend of Linux on
: Mission Critical application.
: Several years ago, - 1997 to be exact, - on a conference I attended
: someone from RedHat gave a speech. In the speech, the guy commented on
: Linux had (at that time) achieved 99.9% uptime, and Red Hat was aiming
: for 99.99999% ( Seven-9s ) uptime before failure.

Seven-9s is 0.1 parts-per-million down. 3 seconds down a year.

If you really need that performance from a system, you'd better spend
alot of effort on _all_ parts of the system (multiple independant
power, cooling and network) and have multiplem machine & site redundancy.

Improving the OS from 99.9% to 99.999...% will help little if the
network or power is only 99%.

Are you also _sure_ that uptime is the important metric? Usually,
people are willing to wait a few seconds. Data loss can be a big
problem, particularly if it isn't indentified at the time.

In this respect, perhaps ext2 and journalling have brought Linux
up to the level of *BSD with SoftUpdates. AFAIK, MS-Windows
has always done very limited write-caching because of the known
unreliability of the OS. I don't know if later versions of NT
are tuned for more caching. Of course, if you're really paranoid,
you run a slow sync filesystem.

-- Robert

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