[talk] ZFS v UFS on APU2 msata SSD with FreeBSD

Brian Reynolds nycbug-talk at reynolds.users.panix.com
Fri May 17 16:43:51 EDT 2019

Charles Sprickman wrote:
> > On May 17, 2019, at 10:23 AM, Isaac (.ike) Levy
> > <ike at blackskyresearch.net> wrote:
> > On Fri, May 17, 2019, at 10:11 AM, George Rosamond wrote:
> >>
> >>  Does it make sense?  Does anyone else have experiences with ZFS
> >> v UFS on APU2s?

So long as you're running 64 bit, I think it makes perfect sense.  Of
course it would be even better if you could squeeze in two SSDs and
mirror them.

> > It's a real delightful combo, IMHO, and great timing- because ZFS
> > memory/implementation is really reliable, (used to *require* so
> > much more RAM and tweaking), nowadays it just works- properly
> > boring.
> Tell me more???  I avoid ZFS on anything without 8GB or more of RAM,
> so I???ve never used it on 512MB/1GB/2GB VPS hosts I have out
> there. Should I be using it?

First off, my background is as a Solaris sysadmin who now concentrates
on FreeBSD.  I have used ZFS on Sun, and other hardware, under Solaris
10, and other OSes, for a number of years.

That said, the memory "requirements" seen in the post-Sun
implementations of ZFS appear to me to be the result of interpreting
the worst case from Sun's already conservative documentation.

The highest of the memory usage requirements (~1GB RAM per TB of
storage) assumed you were running de-dupe, something, as I recall, Sun
eventually recommended people not use.

The other big user of memory is caching.  If the ZFS sub-system sees
that there is available (i.e., unused) memory it will request all of
it.  If it sees that other parts of the system are requesting memory
it will release some of the cache to ease the system's burdens.

So far as tweaking ZFS goes, the most comprehensive document for
fiddling with ZFS internals was known as the "ZFS Evil Tuning Guide".
It's name was chosen to discourage people from fiddling.  The tl;dr is
"Don't do it."  There are better ways to improve system performance.

In addition to bigger machines, I routinely ran Solaris 10 and ZFS on
Sun Blade 100s with at most 4GB RAM and a couple of first generation
IDE hard drives.  I also ran ZFS with FreeBSD 9 & 10 on Dell desktops
with more memory, but room for only one drive.

With that little memory (< 4GB once the OS takes its chunk) some
features will be automatically turned off, but I never missed them.
Even without the data redundancy, ZFS was still a win due to
snapshots, which in turn allow boot environments (under Solaris and
FreeBSD).  Boot environments saved me from bad OS and package updates
on several occasions.

Brian Reynolds -- reynolds at panix.com
"Long ago, it was the way of my people to travel to the Moon. My people
travelled to the Moon in a ship called 'Apollo.' I tell the story of Apollo
in the hope that some day, my people will again travel to the Moon." P. Alway

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