[zfs-discuss] Re: Help with estimated memory need

tbuskey tbuskey at gmail.com
Wed Mar 14 23:47:59 EDT 2012



On Mar 13, 9:40 am, "Fajar A. Nugraha" <l... at fajar.net> wrote:
> It depends.
>
> There were long topics about dedup on zfs-disc... at opensolaris.org, you
> can search the archive if you're interested.
>
> For me, basically it depends on how dedupe-able your data is. If it's
> mostly the same (say, an OS VM template that you'll be using for tens
> of users) then dedup is better. However, if it's "normal" user data
> (e.g. documents, executables, etc) then compression will serve you
> better, so a fast-enough CPU is good investment. If it's
> non-compressible, non-dedupable (e.g. movies, .tar.gz archives) then
> just spend your funds on extra space.
>

> >> On Tue, Mar 13, 2012 at 3:28 PM,  <sw... at petaramesh.org> wrote:
> >> (1) stay away from dedup
> >> (2) stay away from dedup
> >> (3) stay away from dedup :)

I used to run OpenSolaris with a 4x500GB raidz and a 4x750GB raidz on
a 3GB system.  I turned on dedup for the 4x750GB.  My system crashed
due to a power outage.  I kept crashing while doing a zfs import.  I
removed the 4x750GB and still crashed.  I removed the boot drives and
booted from CD and was able to do an import.  So I tried to do the
same with the 4x750GB and CD.  After 36 hours it crashed.  I ended up
using a 2nd computer with 8 GB of RAM and was able to do an import (48
hours).  I was without my data for a week, which is ok in my home
setup.

My dedup ratio was ~ 1.2.  I don't think it was worth it at all.  My
old computers max out at 4GB and 8GB so adding RAM wouldn't help; the
slots are full up.  The only solution is a new motherboard that
supports more RAM.  That probably means replacing everything else too.

I've seen lots of posts that say "ram is cheap, add more".
Motherboards that can go to 32GB start at $80 + CPU $125 + 8GB RAM $50
= $255.  Assuming I have a case & power supply that work with it,
work, that's not too bad.  For a MB that goes to 64GB, you're at $400
to build an 8GB system.  For those looking at an atom, aren't those 32
bit & max out at 4GB?




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