Alvaro Herrera wrote: > On Wed, Sep 14, 2005 at 11:28:43AM -0700, Jeffrey W. Baker wrote: > >>On Wed, 2005-09-14 at 11:25 -0700, Peter Darley wrote: >> >>> I'm getting a new server for our database, and I have a quick question >>>about RAID controllers with a battery backed cache. I understand that the >>>cache will allow the cache to be written out if the power fails to the box, >>>which allows it to report a write as committed safely when it's not actually >>>committed. >> >>Actually the cache will just hold its contents while the power is out. >>When the power is restored, the RAID controller will complete the writes >>to disk. If the battery does not last through the outage, the data is >>lost. > > > Just curious: how long are the batteries supposed to last? >
The recent *cheap* version of a ramdisk had battery backup for 16 hours. (Very expensive ramdisks actually have enough battery power to power a small hard-drive to dump the contents into). I'm guessing for a RAID controller, the time would be in the max 1 day range. John =:->
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