should TRIM be working on my ZFS L2ARC devices?

[Dan Mack]

Hiya,

Hopefully a simple question on TRIM + ZFS,

I have a couple L2ARCs for a zpool on a test box, two different SSDs:

ada0 at ahcich0 bus 0 scbus0 target 0 lun 0

ada0: <OCZ-VERTEX4 1.5> ATA-9 SATA 3.x device

ada0: 600.000MB/s transfers (SATA 3.x, UDMA6, PIO 8192bytes)
ada0: Command Queueing enabled
ada0: 122104MB (250069680 512 byte sectors: 16H 63S/T 16383C)
ada0: Previously was known as ad4
ada1 at ahcich1 bus 0 scbus1 target 0 lun 0

ada1: <INTEL SSDSC2CW120A3 400i> ATA-9 SATA 3.x device

ada1: 600.000MB/s transfers (SATA 3.x, UDMA6, PIO 8192bytes)
ada1: Command Queueing enabled
ada1: 114473MB (234441648 512 byte sectors: 16H 63S/T 16383C)
ada1: Previously was known as ad6

I'm just using a small piece of each one for the L2ARC per below:

                 capacity     operations    bandwidth
pool         alloc   free   read  write   read  write
-----------  -----  -----  -----  -----  -----  -----
tron         98.2G  3.53T      7     23  58.2K   970K
   mirror     49.1G  1.76T      3     11  29.2K   485K
     ada2         -      -      1      5  15.4K   485K
     ada4         -      -      1      5  14.7K   485K
   mirror     49.1G  1.76T      3     11  29.0K   485K
     ada3         -      -      1      5  14.6K   485K
     ada5         -      -      1      5  15.3K   485K
cache            -      -      -      -      -      -
   gpt/larc0  2.89G  29.1G      0      5      9   201K
   gpt/larc1  2.12G  29.9G      0      1      9   148K
-----------  -----  -----  -----  -----  -----  -----

I'm running 10.0-CURRENT #34 251520 and I never seen any successful trim 
events:

kstat.zfs.misc.zio_trim.bytes: 0
kstat.zfs.misc.zio_trim.success: 0
kstat.zfs.misc.zio_trim.unsupported: 102
kstat.zfs.misc.zio_trim.failed: 0

kstat.zfs.misc.zio_trim.unsupported is always > 0 and the other values 
stick at 0.

Does the Vertex 4 and Intel 520 not work with TRIM on FreeBSD or is 
something else going on here?  Like, will TRIM only kick in after each 
device gets full and pages start getting evicted ?

Thanks!

Dan