On Mon, 3 Dec 2007, Martin Marques wrote:
> Out of ignorance, do RAID devices have write cache? I'm talking about
> RAID through hardware.
Depends on the device. There are hardware RAID cards with cache, and ones
without. Generally the ones with cache allow you to adjust whether the
cache is used or not ("write-back"=used and "write-through"=unused). If
you're using it, you should have a battery installed lest the system get
interrupted while data is in the cache (and presumed written by the
database) but not written to disk yet.
Some cards allow you to adjust whether the individual disks utilize their
cache or not. For database use, if you're using the controller cache to
preserve writes, you should make sure the individual disk caches are
turned off.
--
* Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD