On Wed, 2 Apr 2008, James Mansion wrote:
I'm well aware that there are battery-backed caches that can be detached from controllers and moved. But you'd better make darn sure you move all the drives and plug them in in exactly the right order and make sure they all spin up OK with the replaced cache, because its expecting them to be exactly as they were last time they were on the bus.
The better controllers tag the drives with a unique ID number so they can route pending writes correctly even after such a disaster. This falls into the category of tests people should do more often but don't: write something into the cache, pull the power, rearrange the drives, and see if everything still recovers.
You would think hard drives could have enough capacitor store to dump cache to flash or the drive - if only to a special dump zone near where the heads park. They are spinning already after all.
The free market seems to have established that the preferred design model for hard drives is that they be cheap and fast rather than focused on reliability. I rather doubt the tiny percentage of the world who cares as much about disk write integrity as database professionals do can possibly make a big enough market to bother increasing the cost and design complexity of the drive to do this.
-- * Greg Smith gsmith@xxxxxxxxxxxxx http://www.gregsmith.com Baltimore, MD -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
