Bernd Walter ticso at cicely7.cicely.de
Sat Feb 23 14:32:16 UTC 2019

On Fri, Feb 22, 2019 at 08:59:10AM -0700, Ian Lepore wrote:
> On Fri, 2019-02-22 at 17:38 +0200, Stefan Parvu wrote:
> > I know ZFS would need a decent amount of RAM to start with. So for
> > such low sized 
> > SBC systems, like Raspberry PI having ZFS for root might be no go.
> > 
> > What I meant was: how complicated would be right now for FreeBSD 12
> > to have an 
> > ARM64 RBPI3B+ image image which could use ZFS to boot from a SD Card.
> > 
> > Stefan Parvu
> > sparvu at kronometrix.org
> > 
> > 
> People have run a 512MB beaglebone with zfs on sdcard. It surely wasn't
> high performance, and it reported needed some hand-tuning to run at
> all, but it worked.

The only hand tuning is vfs.zfs.arc_max.
Otherwise it just works.
I've went down to 128MB without noticeable problems, but never went
below 256MB in the long run.

But most of my zroot arm systems are 2GB RAM once, either Wandboard-Quad
or Pine64-LTS.

This is from a Pi1 with 256MB arc_max:
last pid: 48345;  load averages:  0.00,  0.00,  0.00  up 4+16:57:58  15:28:14
342 threads:   3 running, 321 sleeping, 18 waiting
CPU: -3.1% user,  0.0% nice,  3.3% system,  0.7% interrupt, -0.5% idle
Mem: 4252K Active, 207M Inact, 4468K Laundry, 145M Wired, 20M Buf, 64M Free
ARC: 20M Total, 7162K MFU, 6336K MRU, 32K Anon, 672K Header, 6357K Other
     2284K Compressed, 11M Uncompressed, 4.92:1 Ratio

It is a local ntp server, so no high memory load from processes.

> There's a lot of mythology about sdcards and what they can and can't
> do, and how supposedly fragile they are.  It's all a bunch of noise you
> can safely ignore.  They're slow, but they're plenty reliable.

Reliable, unless you power cycle them...
Since they have to refresh data after several reads, they can even fail
after a powercycle in the wrong situation when your system mounts them
The only cards which, so far, never have failed for me with power cycles
are SanDisk Extreme plus.
I can really suggest them for anything with random write loads on them,
but they are pricey compared to other cards.
I doubt they are power cycle proof either, but with fast writes they are
less likely to see a power cycle in a bad moment.
I know that there are power cycle proof cards available, e.g. from Swiss Bits,
but AFAIK non of them make them as uSD cards.

B.Walter <bernd at bwct.de> http://www.bwct.de
Modbus/TCP Ethernet I/O Baugruppen, ARM basierte FreeBSD Rechner uvm.

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