On Mon, Jul 30, 2012 at 8:58 AM, Roy Sigurd Karlsbakk <r...@karlsbakk.net> 
>> >  For several times now I've seen statements on this list implying
>> > that a dedicated ZIL/SLOG device catching sync writes for the log,
>> > also allows for more streamlined writes to the pool during normal
>> > healthy TXG syncs, than is the case with the default ZIL located
>> > within the pool.
>> After reading what some others have posted, I should remind that zfs
>> always has a ZIL (unless it is specifically disabled for testing).
>> If it does not have a dedicated ZIL, then it uses the disks in the
>> main pool to construct the ZIL. Dedicating a device to the ZIL should
>> not improve the pool storage layout because the pool already had a
>> ZIL.
> Also keep in mind that if you have an SLOG (ZIL on a separate device), and 
> then lose this SLOG (disk crash etc), you will probably lose the pool. So if 
> you want/need SLOG, you probably want two of them in a mirror…

That's only true on older versions of ZFS.  ZFSv19 (or 20?) includes
the ability to import a pool with a failed/missing log device.  You
lose any data that is in the log and not in the pool, but the pool is

Freddie Cash
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