recommended memory for zfs

[Dan Nelson]

In the last episode (May 09), Benjamin Adams said:
> Hello zfs question about memory.
> I heard zfs is very ram hungry.
> Service looking to run:
> - nginx
> - postgres
> - php-fpm
> - python
> 
> I have a machine with two quad core cpus but only 4 G Memory
> 
> I'm looking to buy more ram now.
> What would be the recommend amount of memory for zfs across 6 drives on 
> this setup?

As much as is reasonable to purchase.  Postgres would probably appreciate
the memory more than ZFS.  You can run ZFS on memory-limited machines (I've
gone as far down as 256MB), but the critical part is running a 64-bit
kernel.  ZFS does a lot of kernel malloc/free operations, and address space
fragmentation on a 32-bit system will eventually cause a panic when ZFS
can't malloc a contiguous 128k chunk.

-- 
	Dan Nelson
	dnelson at allantgroup.com