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Orthogonal elements

Orthogonal elements

Posted Apr 30, 2008 12:20 UTC (Wed) by nix (subscriber, #2304)
In reply to: Orthogonal elements by NAR
Parent article: Ksplice: kernel patches without reboots

Because it may be really *expensive*.

Fundamentally, if ever a system is taken out of service, whatever redundancy mechanisms may be
in place may happen to fail then. Thus it is wise to reduce the time for which a machine is
out of service. ksplice can, for a large proportion of smaller patches, reduce this period to
a fraction of a second, with no loss of non-persistent state.

And that seems worthwhile to me.


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Orthogonal elements

Posted Apr 30, 2008 12:48 UTC (Wed) by NAR (subscriber, #1313) [Link]

Because it may be really *expensive*.

I believe in this case there's no free lunch. I think if a user can't accept a couple of minutes downtime for a reboot, but isn't willing to invest in spare hardware won't really get high availability, only a sense of high availabilty.

I've checked CVE and found 10 linux kernel problems for this year. At this rate there could be 30 such problems in a year - if all problems need a reboot, than that's about 60-90 minutes of downtime. I guess a hardware failure would lead to a longer downtime (it takes time to get the new hardware) and a hardware failure isn't schedulable to off-business or off-peak hours (unlike the kernel change).

To me, this solution looks to be more like a toy (or a weird hack, as it was put earlier in this thread). It's nice, but I wouldn't use it for real.

Orthogonal elements

Posted May 1, 2008 3:56 UTC (Thu) by himi (guest, #340) [Link]

60-90 minutes of downtime for thirty reboots? Hell, I couldn't guarantee that with the tiny
little Dell PE860s I'm working with at the moment - it'd be more like 300 minutes for some of
the larger and more interesting hardware configurations we use in my organisation. Or far
more, when one of those reboots includes an fsck of a multi-terabyte filesystem.

ksplice sounds like a weird kludge at first but I can actually see it being very useful,
particularly for systems running unmodified vendor kernels. It might fail occasionally (and a
1 in 5 failure rate is pretty good for something like this) but that still means 80% fewer
reboots.

himi


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