2. SLOG is only useful for specific use cases, and to do it right requires a special dedicated SSD. See
http://doc.freenas.org/9.10/zfsprimer.html, the section starting with ZFS provides a write cache.
Sorry to sound so stubborn, but having dedicated ssd space really increases the dependability of your fileserver. This is because you don't have to set your smb server to lie about the status of its writes (strict sync = no
).
And, secondly, adding ssd space as log is not the addition log functionality, but replaces the usage of spinning disks as zil device, as mentioned in the articles you quote. Of course, your mileage may vary, whether it substantially affects actual usage and performance has to be seen, but it definitely helps for end to end resilience if your fileserver is able to really do synchronous writes when requested.
My intent was simply to steer the original requester towards a sound, and dependable - yet fast - system. Isn't that nicely in line with the FreeBSD mission statement!
The remarks on pairing RAM-size to L2Arc are valuable; when adding an L2Arc one should certify that the extra ram is available (about 1/40 of the size of your L2Arc, given the mean workload is 8k writes.
https://wiki.freebsd.org/ZFSTuningGuide#L2ARC_discussion), so, for a 120Gb L2Arc about 4Gb of RAM would suffice.
