Scott

     I hope this actually gets to you, given that my questions back in May
went apparently into the bit bucket.
     Please pass the following thoughts along to the person whose question
you read in episode #164 concerned running ZFS on systems with limited (in
a recent sense of the term) memory.

     1) Avoid deduplication.  Deduplication is the main thing in ZFS that
needs the "+ 1 GB RAM / 1 TB of direct access storage" in the memory
recommendations for systems running ZFS.  There may be some obscurely rare
situations in which deduplication's memory gluttony might be restrained
sufficiently to use it on a 1 GB to 8 GB system, but you almost certainly
do not face those situations (assuming there even are such).  IOW, just
don't use it.  You'll get far more benefit from compression than from
deduplication.

     2) There are some sysctl variables you might twiddle with to see whether
they can help:
	vm.kmem_size_max		This one is often all you will need.
					You can usually let ZFS figure out how
					best to co-operate with other kernel
					storage needs within this limit.  ZFS
					will probably bitch loudly during
					boot/startup if you set it slightly
					below 512 MB, but will probably still
					work okay.
Note that the following can only be set when zfs.ko is loaded or ZFS is
compiled into the kernel.
	vfs.zfs.arc_max			This one allows you to limit the size
					of the ARC.  Getting it right for all
					of your system's workloads is not easy
					and is complicated by the fact that it
					must be set in /boot/loader.conf.
	vfs.zfs.prefetch_disable	The default is 1 unless the system's
					memory exceeds 4 GB; must be set at
					boot time like the two above.  Leave
					disabled for systems with little
					memory; it's a performance option you
					can live without in most cases.  If
					you really need fast, sequential read
					performance, you can try setting to 0,
					but you'd be better off getting more
					memory.
	vfs.zfs.vdev.cache.size

     3) Don't use a L2ARC (i.e., a "cache" vdev) because keeping track of its
contents eats up RAM in addition to the ARC's requirements.  Just live with
the memory-resident ARC.  You'll probably find that it's all you actually
need anyway.


                                  Scott