SSD Caching (ZIL/L2ARC)

[grantd]

I know the usual just as more RAM, but if that is not an option...I was wondering if it is possible to use 2 SSDs in a ZFS Mirror as the ZIL/L2ARC drive? I currently just use my FreeNAS box as a 20 TB formatted CIFS share with the following specs and have no performance issues:

AMD Athlon 5350 APU 4-core at 2.06 GHz
16 GB RAM
LSI00244 (9201-16i)
15 2TB SATA drives in RAID-Z2 with a hot-spare


Just to reiterate, no performance issues. My network read/writes run at about 90 MB/s (1 Gbps full duplex is great) and if I go to shell, a copy of a large (100 GB+ files) averaged at 147 MB/s. Just more of a wondering thing as my system board only has 2 memory slots, so 16 GB is the max I can put in without spending a large amount of money for 16/32 GB DIMMS.


Thanks in advance.

 

[Vito Reiter]

This article HERE by @cyberjock explains the use of ZIL/L2ARC very well. If you're not experiencing performance issues I wouldn't worry about it (Don't fix what's not broke kind of thing/adding another point of failure). All your specs look great, however, it is unrecommended to have more than 11 drives in a single vdev if all of those drives are in a single RaidZ2.

 

[grantd]

Thanks for the reply Vito. Just thinking long term if I notice things in the future.

As for the 11 drive vdev thing, my system syncs to a second system which then backs up to tape on a regular basis, so I am not worried about data loss. Overkill for a home setup....but works great.

 

[Vito Reiter]

Thanks for the reply Vito. Just thinking long term if I notice things in the future.

As for the 11 drive vdev thing, my system syncs to a second system which then backs up to tape on a regular basis, so I am not worried about data loss. Overkill for a home setup....but works great.

There is no such thing as overkill when it comes to your data, good job with the backups and read through that PDF it helped me infinitely when I started with FreeNAS.

 

[grantd]

I remember reading something just like this when I did my NAS over a year ago, it was a PowerPoint doc and it helped a lot. Forgot it went over the ZIL and L2ARC as most things I read just said to add more memory and only briefly went over SSD caching.

Thanks again

 

[Stux]

Thing about l2arc is it requires more ram to maintain the l2arc tables which say what is where on l2arc.

Zil only benefits sync writes. If you're not experiencing poor performance with sync writes (nfs/iscsi) then you don't need one.