On 27 Oct 2005, at 14:57, Tom Lane wrote:
> Alex Stapleton <alexs@advfn.com> writes:
>
>> suspicion is that if the power failure isn't a particularly fast one,
>> (e.g. you overloaded a fuse somewhere, fuses are insanely slow to
>> fail compared to alternatives like MCBs) then your RAID card's RAM
>> will get corrupted as the voltage drops or the system memory will
>> resulting in bad data getting copied to the RAID controller as RAM
>> seems to be pretty sensitive to voltage variations in experiments
>> i've done on my insanely tweak-able desktop at home. I would of
>> though ECC probably helps, but it can only correct so much.
>>
>
> Any competently designed battery-backup scheme has no problem with
> this.
>
> What can seriously fry your equipment is a spike (ie, too much voltage
> not too little). Most UPS-type equipment includes surge suppression
> hardware that offers a pretty good defense against this, but if you
> get
> a lightning strike directly where the power comes into your building,
> you're going to be having a chat with your insurance agent. There is
> nothing made that will withstand a point-blank strike.
>
The system RAM won't usually be supported by any batteries though, so
it will go crazy, copy corrupt data to the DIMMs on the RAID
controller, which then will refuse to write it to the disk until the
power comes up, and then write the bad data to the drive surely?