ZFS: How to enable cache and logs.

[Daniel Kalchev]

On 11.05.11 13:51, Jeremy Chadwick wrote:
>
> Furthermore, TRIM support doesn't exist with ZFS on FreeBSD, so folks
> should also keep that in mind when putting an SSD into use in this
> fashion.
>
By the way, what would be the use of TRIM for SLOG and L2ARC devices?
I see absolutely no benefit from TRIM for the L2ARC, because it is 
written slowly (on purpose). Any current, or 1-2 generations back SSD 
would handle that write load without TRIM and without any performance 
degradation.

Perhaps TRIM helps with the SLOG. But then, it is wise to use SLC SSD 
for the SLOG, for many reasons. The write regions on the SLC NAND should 
be smaller (my wild guess, current practice may differ) and the need for 
rewriting will be small. If you don't need to rewrite already written 
data, TRIM does not help. Also, as far as I understand, most "serious" 
SSDs (typical for SLC I guess) would have twice or more the advertised 
size and always write to fresh cells, scheduling an background erase of 
the 'overwritten' cell.

Does Solaris have TRIM for ZFS? Where? How does it help? I can imagine 
TRIM for the data pool, that would be good fit for ZFS, but SSD-only 
pool.. are we already there?

Daniel