ZFS: How to enable cache and logs.

[Bob Friesenhahn]

On Thu, 12 May 2011, Danny Carroll wrote:
>
> Replying to myself in order to summarise the recommendations (when using
> v28):
> - Don't use SSD for the Log device.  Write speed tends to be a problem.

DO use SSD for the log device.  The log device is only used for 
synchronous writes.  Except for certain usages (E.g. database and NFS 
server) most writes will be asynchronous and never be written to the 
log.  Huge synchronous writes will also bypass the SSD log device. 
The log device is for reducing latency on small synchronous writes.

> - Is there any advantage to using a spare partition on a SCSI or SATA
> drive as L2Arc?  Assuming it was in the machine already but doing nothing?

The L2ARC is intended to reduce read latency and is random accessed. 
It is unlikely that rotating media will work well for that.

Bob
-- 
Bob Friesenhahn
bfriesen at simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/