On 09/26/2012 01:14 PM, Edward Ned Harvey
(opensolarisisdeadlongliveopensolaris) wrote:
>> From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss-
>> boun...@opensolaris.org] On Behalf Of Jim Klimov
>> Got me wondering: how many reads of a block from spinning rust
>> suffice for it to ultimately get into L2ARC? Just one so it
>> gets into a recent-read list of the ARC and then expires into
>> L2ARC when ARC RAM is more needed for something else, 
> Correct, but not always sufficient.  I forget the name of the parameter, but 
> there's some rate limiting thing that limits how fast you can fill the L2ARC. 
>  This means sometimes, things will expire from ARC, and simply get discarded.

The parameters are:

 *) l2arc_write_max (default 8MB): max number of bytes written per
    fill cycle
 *) l2arc_headroom (default 2x): multiplies the above parameter and
    determines how far into the ARC lists we will search for buffers
    eligible for writing to L2ARC.
 *) l2arc_feed_secs (default 1s): regular interval between fill cycles
 *) l2arc_feed_min_ms (default 200ms): minimum interval between fill

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