Few minor things.<p>ARC actually is optional, and in fact FreeBSD disables it by default if you have less than 2GB RAM.<p>1GB per TB or more like 5GB per TB is rule of thumb if you use deduplication. If you don&#x27;t use deduplication it&#x27;s more of: &quot;the more RAM you have the better performance you get for reading&quot;<p>ARC is not for writing. It&#x27;s purely used for improving read performance. For improving write performance you use ZIL device. ZIL is essentially a journal. If you don&#x27;t specify ZIL device ZFS will store it on data disks. If writing performance is important it is recommended to keep ZIL on separate device (especially SLC SSD). More about ZIL: <a href="http:&#x2F;&#x2F;nex7.blogspot.com&#x2F;2013&#x2F;04&#x2F;zfs-intent-log.html" rel="nofollow">http:&#x2F;&#x2F;nex7.blogspot.com&#x2F;2013&#x2F;04&#x2F;zfs-intent-log.html</a>