# ARC size and memory size



## yom (Sep 10, 2013)

I'm going to use some servers with 32 GB of RAM. I've been doing some testing with this while one of these server was only with 16 GB of RAM, and what we technically need is that ZFS should not use all the free space. I mean that we could let ZFS have at most 16 GB to play, but we would like to have the other 16 GB free for something else. I've watched the ZFSTuningGuide on the FreeBSD Wiki, and I could see that it is possible to tell ARC to use not everything. Would such configuration in the boot loader.conf be sufficient to tell ZFS to use only 16 GB:

```
vfs.zfs.arc_max="16G"
```
or would I need to configure anything else for ZFS to only use 16 GB?


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## kpa (Sep 10, 2013)

The ARC cache is a special case with the memory management. It uses "wired" memory that can not be swapped out under any circumstances. The "everything else" you'll be running on the system uses the normal virtual memory that can be swapped when needed so you don't have to do anything special, just limit ARC cache to a suitable amount.


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