Performance of a USB ZIL for ZFS

[Robert Simmons]

On 25 Jun 2011, at 19:17, Joshua Isom<jrisom at gmail.com>  wrote:
> I was wondering if anyone had tried using a decent USB flash drive for
> the ZIL.  I know it'd be hard finding one fast enough, but some from
> patriot seem like they might be suitable for home use.  Part of the
> idea is to just minimize hard drive thrashing and the wear and tear
> associated with it.  If it helps prevent the drives from going bad,
> and doesn't hurt performance too bad all the better.  But if it's
> going to hurt performance too much or not help prevent thrashing
> there isn't a point.

You question is a good one, but I think the reason for your question may be 
off.  If you want the ZIL in a separate location it is to cut down on latency 
rather than "thrashing".  See:
http://www.solarisinternals.com/wiki/index.php/ZFS_Evil_Tuning_Guide#Disabling_the_ZIL_.28Don.27t.29

If your concern really really is "thrashing" please consider the cost of flash 
memory vs a hard drive.  Replacing a bad hard drive is cheaper.  After a 
cursory glance at newegg, you can see the price per MB for:
HDD $0.09
USB flash $0.64
SSD $1.875