On Sun, Jan 08, 2012 at 06:25:05PM -0800, Richard Elling wrote:
> ZIL makes zero impact on resilver.  I'll have to check to see if L2ARC is 
> still used, but
> due to the nature of the ARC design, read-once workloads like backup or 
> resilver do 
> not tend to negatively impact frequently used data.

This is true, in a strict sense (they don't help resilver itself) but
it misses the point. They (can) help the system, when resilver is
underway. 

ZIL helps reduce the impact busy resilvering disks have on other system
operation (sync write syscalls and vfs ops by apps).  L2ARC, likewise
for reads.  Both can hide the latency increases that resilvering iops
cause for the disks (and which the throttle you mentioned also
attempts to minimise). 

--
Dan.

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