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FreeNAS needed memory

Abula

Abula

[H]ard|Gawd
Joined
Oct 29, 2004
Messages
1,036
Hi,

I'm considering building a new setup with FreeNAS, but from what i read there is a recommendation of 1GB per 1TB of storage, so for planning a 16x 8tb will net around 119TB, so going by the recommendation i would need 119GB of memory, now 1151 mobos only come with 4 slots, so at the most i could reach 64gb, will it work fine? or if not, the option would be to plan on LGA 2011-3 / Threadripper, but with the memory pricing of today.... it would be very expensive to go into 128gb ddr4 ecc.

Thanks for your replies,
 
so going by the recommendation i would need 119GB of memory
Click to expand...

You only need 1GB per TB if you are using deduplication.


At work I am using less than 250MB per TB of data on some of my zfs servers (yes even production ones).
 
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Any modern 64bit OS requires around 1-2GB RAM to be stable, does not matter if its Linux, Unix (BSD, Solaris) or Windows or a filesystem size. Oracle claims 2GB as minimum for Solaris 11.3. ZFS itself does not really add any memory needs beside that its internal memory management is Solaris based what means that you need a little more RAM to run ZFS on non-Solaris systems.

Even if you ignore the special RAM needs of realtime dedup in ZFS, you use ZFS, a CopyOnWrite filesystem. This means that your datablocks are spread over the whole pool and especially on a quite full pool your fragmentation can become huge what makes ZFS slower than older filesystems especially as you must write/read more data due the checksums. Security has its price.

You can use ZFS with 2-3GB RAM on any OS without stability problems. But his can mean that your performance falls to the iops performance for random writes/reads of your pool. This can be really worse like the 3MB/s that I have seen on an older WD green. With enough RAM you can use a rambased writecache (default 4GB) and use the rest as rambased readcache for random reads. If you only want to read cache the metadata in RAM, you need around 1% of active data as RAM size on top the 2-3 GB for the OS. A ZFS server with enough RAM delivers most random reads from RAM. For sequential reads you can add an L2ARC for read ahead.

This is why you want at least 4-8GB RAM for a ZFS server with some workloads are happy with 128GB RAM or more. Add the needed RAM for dedup ontop.


https://forums.servethehome.com/ind...m-or-readcache-disabled-and-slow-disks.12170/
 
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Freenas forums are borderline hysterical about high ram requirements and ECC.

Both are nice, neither are required. For a home pool, even a big one, 32-64GB is plenty. More won't hurt but ram is in full cartel price mode now and for the near future.
 
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