Re: ZFS

[Swift Griggs <swiftgriggs%gmail.com@localhost>]

On Thu, 3 Mar 2016, coypu%SDF.ORG@localhost wrote:
> Someone on IRC implied that he is using ZFS. Still struggling to 
> believe, so I gotta ask - is there anyone out there using it?

I'm not. I never knew it got past the idea stage for NetBSD. It's listed 
on the projects page here:

https://wiki.netbsd.org/projects/project/zfs/

Did it ever get to the point where it was usable? The last note on the 
project page says "It is not finished. Ask on tech-kern for more 
information about the current state." but it's dated 2014.

Like you, I wonder about ZFS in general. Didn't the NetBSD project pay 
someone to complete it or am I wrong and it was a purely volunteer effort? 
Was it part of a Google SoC project? Can it ever be pulled into the 
mainline code (ie.. isn't the CDDL incompatible with the BSD license?) ?

ZFS has some great features. I've used it quite a bit under Solaris and 
FreeBSD. However, it's also proven to be a source of a lot of crashes I've 
seen under both (but especially FreeBSD).

I'm guessing it'd be a really big challenge to re-implement things like 
deduplication or other key ZFS features, but then again I look at HAMMER 
and wonder... Since HAMMER is BSD-focused (and BSD licensed) maybe that's 
a better choice to want to throw in with ? Then again, I don't know the 
politics of that, either.

A few tidbits about ZFS:

* Solaris never has had LVM. Sun had a history of making spectacularly
  bad choices before ZFS came along. Those of you who have tried to
  recover a mis-matched SDS/SVM rig know what I mean. They had a chance to
  get VxVM on the cheap in the 90's and pooched it (while HP-UX, Tru64,
  and UnixWare snatched it up). So, NetBSD has RAIDframe which works
  nicely, and now a very sweet LVM. The urgency to have something like ZFS
  in NetBSD shouldn't be quite as acute as it was in Slowlaris.

* I don't consider having block storage commands separated from file
  system commands a weakness. Ie.. LVM + FS == ZFS && ! ZFS > everything.
  I think that puts me on the outs with the cool kids.

* If you put all the storage features in NetBSD up against ZFS, the main
  things you come up missing on are:

  - Huge sizes on all the upper limits. The "zettabyte" part is real.
  - Deduplication
  - online fsck (scrub)
  - An unprecedented level of paranoia about data integrity

However, of those only deduplication is all that exciting. Other ZFS-like 
features we have (if you consider the full NetBSD toolset):

  - Block device encryption
  - Ability to grow a file system (don't think UFS in NetBSD can shrink)
  - Block device abstraction, aggregation / RAID (LVM / RAIDframe)
  - File system snapshots
  - Root disk mirroring

Other stuff I'm not sure about:

  - Can NetBSD do RAID6 / RAID-DP in software ?
  - What about the ZIL and L2ARC, are there already NetBSD equals?
  - Does NetBSD's LVM support multiple copies of an LV on physical PVs
    ala ZFS ditto blocks ?
  - Does anyone care that ZFS is now closed source and the CDDL forks are
    now going to drift significantly from the parent core ? I don't
    really, but I'm just wondering if that's a concern.
  - Do we have anything against HAMMER ? I personally think it's cool.

It's an interesting topic to me.

-Swift