> From: zfs-discuss-bounces@xxxxxxxxxxxxxxx [mailto:zfs-discuss-
> bounces@xxxxxxxxxxxxxxx] On Behalf Of Joe Auty
> I'm also noticing that I'm a little short on RAM. I have 6 320 gig
> drives and 4 gig of RAM. If the formula is POOL_SIZE/250, this would
> mean that I need at least 6.4 gig of RAM.
> What role does RAM play with queuing and caching and other things which
> might impact overall disk performance? How much more RAM should I get?
Excess ram accelerates everything. There is no such thing as a "rule of
The OS will cache everything it's read before, whenever it can (the memory
isn't requested for some other purpose). To avoid having to fetch it a 2nd
time from disk. The OS will also buffer all writes in memory, and attempt
to optimize for the type of storage available, before pushing it out to
disk. (Sync writes will hit the ZIL, stay in ram, and then hit the disk
If you have compression or dedup enabled, these benefit enormously from
Everything is faster with more ram. There is no limit, unless the total
used disk in your system is smaller than the available ram in your system
... which seems very improbable.
The more ram, the better. Choose how much money you're willing to spend,
and spend that much on ram.
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