battery question

[Ben Scott]

On Thu, Jun 11, 2009 at 1:38 PM, Preston Hagar<prestonh at gmail.com> wrote:
> If I remember Dell PERC terminology correctly, write back uses the
> cache and write through does not.

  You are correct.  "Write through" means the rights go straight
through the cache to the disk.  "Write back" means the writes are held
back until it's convenient to write them.  Reads are always cached.

  In write-back mode, it's possible for the controller to re-order
writes for efficiency; I don't know if any particular PERC does so.

> Secondly, if you have the server on a good reliable UPS, then it isn't
> quite as big of a concern, although it is still a possible one.

  Also deserving of mention, in addition to UPS failures:

* Power supply/bus faults in the server itself
* Power cord accidentally disconnected
* Power switch accidentally turned off

-- Ben