I am about to install TrueNas Core on a XEON 1390 computer. I watched the below episode and am now considering installing 2 OPTANE drives (mirrored) for a SPECIAL META DATA pool. How do I determine the amount of storage to use? I think it was related to the max number of files you could store on the data pool?
I have the same question about how to decide how much ARC RAM to install. Also can you allocate how much of system RAM to set aside for ARC or does it just dynamically adjust it based on how much RAM the system needs at any point in time? THANKS!!!
ZFS takes most of free RAM for ARC and gives it back to the OS if other applications need it. More ARC is more better. ARC caches data and metadata after all, aside from numerous other things…so memory is fairly important for ZFS to deliver performance.
ARC grows and shrinks dynamically…it acts like your normal OS page cache in that regard. It’s totally transparent and ARC takes what is available. You can set upper and lower limits to ARC if necessary, but most of the time it runs just fine without tweaking.
People are usually concerned about this because ARC doesn’t show up as “free memory” while pagecache does. It’s just a matter of display and perception, not function. I’ve yet to see people disabling or limiting their pagecache in Windows or Linux.
DRAM is Life, baby!
General recommendation is 1GB of ARC for 1TB of storage. It’s a rule of thumb and general guideline. Means there are also a lot of pools out there with 40TB of data that make efficient use of 256GB of ARC. And 8GB ARC runs on 100TB pools, just don’t expect miracles or any noticeable amount of caching.
ARC+L2ARC are the most important things for ZFS outside drives themselves.
It’s a percentage of your stored data. Generally, it ranges roughly between 1-4%.
