Bad ZFS performance on the desktop

[Erik Lauritsen]

I normally only use ZFS for a storage server, but decided to give it
a try on the desktop.

I have installed FreeBSD 12.1 on ZFS root in a mirror with 2 x 1TB
drives for desktop usage.

The performance is terrible every time I use a browser. I suspected the
browser cache to be the problem, so I made a tmpfs and put the cache
there, but the problem is that browsers write to disk all the time and
not only when using the cache.

As soon as I shut down the browser, and I have tried with Firefox and
others, then the harddrives stops working (I can hear the noise).

The browsers are the worst, but other applications that write some
stuff to disk is also not so good.

I understand that ZFS has to write every single bit to disk twice
because I run a mirror, but I am surprised at the performance
penalty and how much these drives keep working.

I have monitored ZFS using 'top' and can see that it never eats
more than half of my memory, so it's not because I'm out of
memory.

I'm thinking about getting a couple of SSDs, but then again I use
backup meticulously and perhaps ZFS on a single drive or just UFS
is better for the desktop?

Any advice would be greatly appreciated.

Kind regards,
Erik