I did try to set up L2ARC on SSD, which is also a boot drive (osx 10.8.1):
/dev/disk1
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *480.1 GB disk1
1: EFI 209.7 MB disk1s1
2: Apple_HFS ROOT 417.3 GB disk1s2
3: Apple_Boot Recovery HD 650.0 MB disk1s3
4: Apple_HFS ZIL 10.0 GB disk1s6
5: Apple_HFS L2ARC 51.0 GB disk1s4
Here is the error message:
$ sudo zpool add extra cache /dev/disk1s4
invalid vdev specification
use '-f' to override the following errors:
/dev/disk1s4 is in use by filesystem at "/Volumes/L2ARC"
$ sudo zpool add -f extra cache /dev/disk1s4
diskutil eraseVolume failed, exit status 1
What am i doing wrong? Is it possible to set up L2ARC on partition?