Re: Extremely Slow Database Import Due to Disk Cache?
From: Elias (nospam_at_charter.net)
Date: 06/21/03
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Date: Fri, 20 Jun 2003 16:55:06 -0700
Will Greene wrote:
> Hello,
> I am having an extremely long processing time for a small oracle
> database to import. I am running on a SunE450 with 2 cpu's at 300Mhz and 2
> channel raid 5. The import file is only 2.5Gbs and should normally require
> only 2-3 hours to import.
>
> When I bring up the config for the DPT controller, I get an error message of
> "Cache is in Write-Through Mode because ... or battery is in Maintenance
> Mode".
> Click [Ok] and the battery status says "initial configuration discharge" or
> somesuch.
> Any idea of what's going on? Could this be the culprit why disk i/o taks
> take sooooo long?
>
> Thanks,
> Will
Yes the cache mode is causing slow performance. Using write-through
sends all data straight through the cache immediately to disk. Your
DPT/Adaptec system is a type of storage that uses its battery to keep
the data in cache during a power outage, then write to disk once the
power comes back on. The other type (that yours is not) uses the
battery to write the uncommitted cached data to disk then powers down.
If you were to have a power outage with a drained, malfunctioning, or
expired battery the system might not have enough battery power to out
last a power outage. If you loose battery power during an outage then
the uncommitted data is lost forever. So, write-through protects you
from this scenario.
Your battery will from time to time discharge and recharge itself as
part of a regular preventative maintenance cycle. Assuming everything
is ok with the battery when it comes back to full charge the array
should set the cache back to write-back mode. I'm pretty sure this is
what will happen with your array. So, just give it about 12 hours or so.
Elias
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