Ethan Erchinger wrote:
> correct ratio of arc to l2arc?
from http://blogs.sun.com/brendan/entry/l2arc_screenshots
Thanks Rob. Hmm...that ratio isn't awesome.
TANSTAAFL
A good SWAG is about 200 bytes for L2ARC directory in the ARC for
each record in the L2ARC.
So if your recordsize is 512 bytes (pathologically worst case), you'll need
200/512 * size of L2ARC for a minimum ARC size, so ARC needs to be
about 40% of the size of L2ARC. For 8 kByte recordsize it will be about
200/8192 or 2.5%. Neel liked using 16kByte recordsize for InnoDB, so
figure about about 1.2%.
In this case, if you have about 150 GBytes of L2ARC disk, and are using
8 kByte recordsize, you'll need at least 3.75 GBytes for the ARC, instead
of 2 GBytes. Since this space competes with the regular ARC caches,
you'll want even more headroom, so maybe 5 GBytes would be a
reasonable minimum ARC cap?
-- richard
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