> I'm a little surprised at lack of any discussion of RAID battery backups.
> All RAID enclosures and RAID host-adapters worth their salt have a BBU
>(battery backup unit) option for exactly this purpose.
Yes...but it's only good for a few hours. So if your power outage lasts more than that, then the BBWC (battery backed write cache) is still toast.
On a related note, I've just bought a pair of HP servers (DL380s) and an IBM X3550. It's very annoying that there is no way to buy either of these without hardware raid, nor can the raid card be turned off in the BIOS. For proper reliability, I only really trust software (md) raid in Raid 1 mode (with write caching off). [Aside: this kills the performance for database workloads (fdatasync), though the Intel X25-E SSDs outperform 10k SAS drives by a factor of about 12.]