Solid state drives

[Paul Makepeace]

On Tue, Apr 20, 2010 at 03:23, Peter Corlett <abuse at cabal.org.uk> wrote:
> On 20 Apr 2010, at 10:07, James Laver wrote:
> [...]
>> Or 'on any machine connected to a UPS that's correctly configured to shut the machine down properly'?
>
> Many data centres won't allow this due to safety concerns.

[citation needed]

> Quite right too: if there's a fire, the fire brigade needs everything *off* while they spray water around, and they don't want one annoying rack still live after they've yanked the master switch.

I wonder how big the intersection of datacenters that don't have halon
AND are served by a fire dept that's using water rather than CO2 to
extinguish electrical fires is.

Google machines have per-machine UPS which works pretty well for a
number of reasons,
http://www.datacenterknowledge.com/archives/2009/04/01/efficient-ups-aids-googles-extreme-pue/

Paul

>
>> Or 'on any machine in a datacenter with generators for backup power'.
>
> And hopefully they've remembered to test it regularly, and that somebody remembers to put diesel in the tank and get budget approval for it, and that the transfer switch works, that the UPS can fill-in while the gennie starts, even though we've filled another row of racks since we last tested it. And so on. There are so many single points of failure in the system, it's not funny, and squashing one just moves the problem elsewhere.
>
> Fortunately, we have very reliable mains electricity in (most of) the UK. It's good enough that adding generators and UPSes actually reduces the reliability. I don't bother with a UPS at home any more.
>
> This sort of thing is *hard* which is why sane people pay somebody else to worry about it.
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