Who said it was bad? I thought we were all pretty much in agreement that it was good, and the only thing holding it back from wider adoption into e.g. the Linux kernel was the poison-pill of Oracle's ownership and licensing.
Things like "ZFS needs 1GB of RAM per 1TB of storage" and "it requires that RAM to be ECC" were once common to find online.
These sort of thing seemed to lead to widespread beliefs that it was inefficient, expensive, and fragile. None of that is true, of course, but folks might remember and believe these myths and conclude that it is (or was) bad.
(But it's pretty excellent. I've been using it for about a decade, now. It'd be nice if it fit into the Linux kernel better, but I manage anyway.)
Are they wrong?
More RAM is better -- of course it is. Otherwise-unused RAM can gets used for stuff like caching (such as the ZFS arc), and caches are faster than disks. That's good for performance.
But ZFS isn't really any more thirsty in this way than other filesystems are, unless special features -- stuff that many other filesystems lack entirely, like deduplication -- get used.
And these days, dedup can use an SSD instead of RAM for the heavy lifting so that's not a huge concern either. (Not that I'm recommending dedup; it works and it is reliable, but it doesn't fit very many workloads.)
I would absolutely be comfortable running ZFS with 12TB on 6GB. Or 2GB, for that matter. It's fine. Send it.
I've personally done more with less and had excellent results. No regrets.
(There's ways to tune arc performance, too. As an example, I've got a dataset that is full of many terabytes of Linux ISOs. I don't need that data to be cached...like, ever. If it were to be cached, it would just consume resources that would be better spent elsewhere. But I do want it to be indexed quickly. So I set that dataset to primarycache=metadata and that works great for me.)
No you do not need 16GB simply for a 12TB ZFS array on a plain Linux/FreeBSD box. It'll be faster, but you don't need it.
... because part of the company wanted you to buy their certified systems
The only lawsuit specifically about licensing was from few Linux developers through SFC who disagree with common consensus on how GPL applies in that case and sued Ubuntu for shipping ZFS as a module.
source: used to work for a storage vendor that was marketing a NAS based on ZFS and got credible threats from Netapp to the point that we sought a partnership with Oracle that included indemnification under Oracles settlement with Netapp.
I was just a lowly support engineer so not privy to all the legal details that the executives were dealing with. I too had to just take them at their word.
ETA: I searched a bit. Here's a link
https://www.enterprisestorageforum.com/networking/netapp-thr...
Maybe threats were enough? I certainly wouldn't want to test it myself.
* https://www.theregister.com/off-prem/2010/09/09/oracle-and-n...
* https://www.computerworld.com/article/1585889/opinion-patent...
NetApp originally sued then-independent Sun in 2007, and Sun counter-sued.
Free/TrueNAS/iXsystems has been offering ZFS-based solutions for many years now, and I haven't heard NetApp going after them:
Maybe he was ... they do that sometimes.
I looked around a little. the C&D from Netapp was in ~July 2010 and the partnership and product with Oracle in the Fall (Around the cease fire) and we continued with that (via the Oracle Partnership) through 2011-2015 when the company ran out of cash and laid us all off.