sata raid & write cache state

[Roisin Murphy]

> Head to www.apc.com and look at the UPSes they have there.  They're
> basically lead acid batteries with inverters to put out A/C power when your
> main power feed goes out.

i meant the battery option they sell with some raid controllers, is
this and extra little PSU, that also powers the disks for a while, or
is this just meant to keep the raid controller's cache powered till
the machine boots up again, so it can finish its cache flush?