To answer the questions of if you saw a performance improvement or not, it's much more important that the way in which the zpool is used is exactly the same as what you use it for. In one setting you could see a phenomenal increase in performance. In another setting with the exact same hardware the difference in performance could be minimal.
It's much more important that you read up on ZIL and L2ARC and understand how they work and what they cache and determine if that function works for you. If you simply say you want it because its a "read" cache you do NOT understand how it works.
I'm trying to understand as much as I can, but the intricacies of file system operations sometimes escape me.
My main interest in L2ARC and ZIL is not necessarily raw write or read performance, but rather in helping in situations where there are multiple simultaneous reads/writes by different processes/users.
I have noted a SIGNIFICANT slowdown on my system - for instance - if there is a continuous write in process (like from a backup process writing to the array) if then a user tries to read from it at the same time.
In situations like these I'll get rather high system loads (of approximately 6) with close to 0 CPU load, so it must be binding up on I/O speed.
My theory is that L2ARC will help a lot in this case if whatever the user is trying to read is in the cache, as then the continuous write will not be interrupted.
While I am struggling with the differences between synchronous and asynchronous writes, I'm also hoping a ZIL will help me overcome the relatively slow write speeds of RAIDz2. I don't have any significant databases running off of the array, mostly multiple users storing and requesting files, at the same time as backups may be taking place.
Proposed System (not yet built):
- AMD FX-8120 32GB RAM running VMWare ESXi 5.1
- FreeNAS running as Guest with 2 cores and 16GB RAM assigned
- 3x3TB WD Green drives in RAIDz2
- Potentially (based on this discussion) 20GB Intel 313 ZIL drive and 128GB Larger faster MLC drive for L2ARC
System load is mostly from 4 end users in the house, but we are tasking users.
At any given time, the following could be happening simultaneously:
- 4 users opening, saving and copying files
- Automated backups from clients to NAS (7 computers in house, 3 PC desktops, 3 PC laptops, 1 Apple MacBook Pro)
- Apple MBP running time machine backup to NAS
- rtorrent running and saving data on server (up to 85mbit downstream network speeds)
- NAS being backed up to offsite cloud backup (up to 35Mbit upstream network speeds)
So as mentioned above, I definitely think L2ARC will help me, but will ZIL? Not as certain. For me my focus is on using a combination of RAM/SSD to compensate for the relatively poor simultaneous read/write performance of my WD Green drives.
I Appreciate any feedback