Mulling over MTBF.
becker at scyld.com
Wed Sep 12 11:38:25 EDT 2001
On Wed, 12 Sep 2001, Carlos O'Donell Jr. wrote:
> On a recent trend, I have been discussing with various
> colleagues the aspect of power usage and power saving
> in clusters.
I'm guessing that you have already looked at the Scyld features for
soft-power-down and Wake-On-LAN (WOL) wake-up. Our system has the
advantage that we identify nodes by the station address, and thus already
have the information needed for WOL.
> At first, power saving, through node sleeping or drive
> spin down, seemed like a good idea.
> Though, I am wary about the following effects:
> - Does spindown/spinup on common IDE drives effect MTBF?
Yes. Typical disk drive ratings put the spin-up count equivalent to
about 9 hours of the MTBF. Those numbers are not directly comparable,
but it's a useful number to look at.
Laptop drives are typically set to spin down after a few minutes of idle
time, both because power savings are much more important and because a
stopped drive is more resistant to shocks.
> - Does node sleeping/wakeup cycles effect MTBF for voltage
> supplies on the motherboard? (Or other componenets, through
> relaxation and transients).
Not obviously: the HV side of most ATX power supplies is continuously
powered, so there is no inrush current shock coming out of stand-by
mode. The thermal stress from the varying load is likely the dominant
We have one batch of ATX power supplies that are very likely to fail in
the brown-out conditions around a power failure. Those same supplies
have not failed when the machine is in stand-by mode during power
failures. Yes, the real solution is to get different power supplies,
however this is an example of soft-power-off increasing the MTBF of the
Donald Becker becker at scyld.com
Scyld Computing Corporation http://www.scyld.com
410 Severn Ave. Suite 210 Second Generation Beowulf Clusters
Annapolis MD 21403 410-990-9993
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