ZFS on small systems

Anselm Strauss amsibamsi at gmail.com
Thu Sep 17 14:35:39 UTC 2009

Thanks for your advice, Steve.

I looked a bit at the source code and in
/usr/src/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c and I
found this:

/* set min cache to 1/32 of all memory, or 16MB, whichever is more */
arc_c_min = MAX(arc_c / 4, 64<<18);

Could this mean that 16 MB are already enough to run ZFS?

On Thu, Sep 17, 2009 at 2:26 PM, Steve Bertrand <steve at ibctech.ca> wrote:
> Anselm Strauss wrote:
>> Hi,
>> I'm interested in using ZFS on one of my small systems with 256 MB of
>> RAM and 4 GB flash disk. Since ZFS is now considered production ready on
>> FreeBSD I would like to use it as root filesystem and profit mainly from
>> the cool snapshot features for easy backups.
>> I found multiple recommendations to run ZFS only on systems with enough
>> resources. But is this only a requirement if you want good performance
>> or also for ZFS to function properly at all?
> I've found that on the i386 arch, that at minimum you need 756M of
> memory to do anything really useful. Now, I don't know if this has
> changed or not, but I doubt that the box would be useful for anything
> with only 256M.
> With that said, I can keep a box running at max disk r/w for hours on
> end with 2GB, and 1536M allocated/reserved for ZFS.
> Perhaps however that there have been enhancements introduced that I
> don't know about, that allow ZFS to operate in such a small memory
> address space, but for some reason I doubt it. If I'm wrong, someone
> will let us know ;)
> Steve

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