ZFS: How to enable cache and logs.

[Danny Carroll]

Hello all.

I've been using ZFS for some time now and have never had an issued
(except perhaps the issue of speed...)
When v28 is taken into -STABLE I will most likely upgrade to v28 at that
point.   Currently I am running v15 with v4 on disk.

When I move to v28 I will probably wish to enable a L2Arc and also
perhaps dedicated log devices.

I'm curious about a few things however.

1. Can I remove either the L2 ARC or the log devices if things don't go
as planned or if I need to free up some resources?
2. What are the best practices for setting up these?   Would a geom
mirror for the log device be the way to go.  Or can you just let ZFS
mirror the log itself?
3. What happens when one or both of the log devices fail.   Does ZFS
come to a crashing halt and kill all the data?   Or does it simply
complain that the ZIL is no longer active and continue on it's merry way?

In short, what is the best way to set up these two features?

-D