Wednesday, May 27, 2009

L2ARC Turbo WarmUp

This has been integrated into snv_107.

"The L2ARC warms up at a maximum rate of l2arc_write_max per second,
which currently defaults to 8 Mbytes. This value was picked to minimise
the expense of both finding this data in the ARC, and writing it to current
read-bias SSDs - which maximises workload performance from warm L2ARC devices.

This value isn't ideal if the L2ARC devices are cold or cool - since we'd like
them to warm up as quick as possible. Also, since they are cold - there is
less concern for interfering with L2ARC hits by writing faster.
This also applies to shifts in workload, where the L2ARC is warm with content
that is no longer getting hits - and behaves as like it is cool.

This RFE is to dynamically increase the write rate when the current workload
isn't cached on the L2ARC (either because it is cold, or because the workload
has shifted); and to idle back the write rate when the L2ARC is warm."

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