> It doesn't seem to be well-maintained.
The last commit is from 3 hours ago: https://github.com/zfsonlinux/zfs/commits/master. They have dozens of commits per month. The last minor release, 0.8, brought significant improvements (my favorite: FS-level encryption).
Or maybe this is referred to the 5.0 kernel (initial) incompatibility? That wasn't the ZFS dev team's fault.
> Performance is not that great compared to the alternatives.
There are no (stable) alternatives. BTRFS certainly not, as it's "under heavy development"¹ (since... forever).
> The kernel team may break it at any time, and won't care if they do.
That's true, however, the amount is breakage is no different from any other out-of-tree module, and it unlikely to happen with a patch version of a working kernel (in fact, it happen with the 5.0 release).
> Using it opens you up to the threat of lawsuits from Oracle. Given history, this is a real threat. (This is one that should be high for Linus but not for me - there is no conceivable reason that Oracle would want to threaten me with a lawsuit.)
"Using" it won't open to lawsuits; ZFS has a CDDL license, which is a free and open-source software license.
The problem is (taking Ubuntu as representative) shipping the compiled module along with the kernel, which is an entirely different matter.
---
[¹] https://btrfs.wiki.kernel.org/index.php/Main_Page#Stability_...
Java is GPLv2+CPE. That didn't stop Oracle because, as Linus pointed out in the email, Oracle regards their APIs as a separate entity to their code.
So it's not comparable with GCC; but comparable to forking clang and keeping clang license. I doubt RMS could be able to say anything.
Note that they don't mean "it's unstable," just "there are significant improvements between versions." Most importantly:
> The filesystem disk format is stable; this means it is not expected to change unless there are very strong reasons to do so. If there is a format change, filesystems which implement the previous disk format will continue to be mountable and usable by newer kernels.
...and only _new features_ are expected to stabilise:
> As with all software, newly added features may need a few releases to stabilize.
So overall, at least as far as their own claims go, this is not "heavy development" as in "don't use."
What makes you say that? I've seen plenty of people make this claim based on URE rates, but I've also not seen any evidence that it is a real problem for a 3-4 drive setup. Modern drives are specced at 1 URE per 10^15 bits read (or better), so less than 1 URE in 125 TB read. Even if a rebuild did fail, you could just start over from a backup. Sure, if the array is mission critical and you have the money, use something with more redundancy, but I don't think RAID5 is infeasible in general.
* All localized error are correctable, unless they overlap on different disks, or result in drive ejection. This precisely fixes UREs of non-raid drives.
* If a complete drive fails, then you have a chance of losing some data from the UREs / localized errors. This is approximately the same as if you used no RAID.
As for URE incidence rate - people use multi-TB drives without RAID, yet data loss does not seem prevalent. I'd say it depends .. a lot.
If you use a crappy RAID5, that ejects a drive on a drive partial/transient/read failure, then yes, it's bad, even worse than no RAID.
That being said, I have no idea whether a good RAID5 implementation is available, one that is well interfaced or integrated into filesystem.
It has terrible performance problems under many typical usage scenarios. This is a direct consequence in the choice of core on-disc data structures. There's no workaround without a complete redesign.
It can become unbalanced and cease functioning entirely. Some workloads can trigger this in a matter of hours. Unheard of for any other filesystem.
It suffers from critical dataloss bugs in setups other than RAID5. They have solved a number of these, but when reliability is its key selling point many of us have concerns that there is still a high chance that many still exist, particularly in poorly-exercised codepaths which are run in rare circumstances such as when critical faults occur.
And that's only getting started...
[1] which I used for nearly two years on a small desktop machine on a daily basis; ended up with (minor?) errors on the file system that could not be repaired and decided to switch to ZFS. No regrets, nor similar errors since.
Is bcachefs more-or-less ready for some use cases now? Does it still support caching layers like bcache did?
Regarding caching: "Bcachefs allows you to specify disks (or groups thereof) to be used for three categories of I/O: foreground, background, and promote. Foreground devices accept writes, whose data is copied to background devices asynchronously, and the hot subset of which is copied to the promote devices for performance."
If all you need is a simple root FS that is CoW and checksummed, bcachefs works pretty good, in my experience. I've been using it productively as a root and home FS for about two years or so.
Same for encryption, there are already existing crypto layers both on the block and filesystem (as an overlay) level.
Are you sure about that? Always reading both doubles read I/O, and benchmarks show no such effect.
> there's no way for the fs to tell which is correct
This is not an immutable fact that precludes keeping the RAID implementation separate. If the FS reads data and gets a checksum mismatch, it should be able to use ioctls (or equivalent) to select specific copies/shards and figure out which ones are good. I work on one of the four or five largest storage systems in the world, and have written code to do exactly this (except that it's Reed-Solomon rather than RAID). I've seen it detect and fix bad blocks, many times. It works, even with separate layers.
This supposed need for ZFS to absorb all RAID/LVM/page-cache behavior into itself is a myth; what really happened is good old-fashioned NIH. Understanding other complex subsystems is hard, and it's more fun to write new code instead.
This is all great, and I assume it works great. But it is no way generalizable to all the filesystems Linux has to support (at least at the moment). I could only see this working in a few specific instances with a particular set of FS setups. Even more complicating is the fact that most RAIDS are hardware based, so just using ioctls to pull individual blocks wouldn’t work for many (all?) drivers. Convincing everyone to switch over to software raids would take a lot of effort.
There is a legitimate need for these types of tools in the sub-PB, non-clustered, storage arena. If you’re working on a sufficiently large storage system, these tools and techniques are probably par for the course. That said, I definitely have lost 100GBs of data from a multi-PB storage system from a top 500 HPC system due to bit rot. (One bad byte in a compressed data file left the data after the bad byte unrecoverable). This would not have happened on ZFS.
ZFS was/is a good effort to bring this functionality lower down the storage hierarchy. And it worked because it had knowledge about all of the storage layers. Checksumming files/chunks helps best if you know about the file system and which files are still present. And it only makes a difference if you can access the lower level storage devices to identify and fix problems.
Why not? If it's a standard LVM API then it's far more general than sucking everything into one filesystem like ZFS did. Much of this block-mapping interface already exists, though I'm not sure whether it covers this specific use case.
At the time that ZFS was written (early 2000s) and released to the public (2006), this was not a thing and the idea was somewhat novel / 'controversial'. Jeff Bonwick, ZFS co-creator, lays out their thinking:
* https://blogs.oracle.com/bonwick/rampant-layering-violation
Remember: this was a time when Veritas Volume Manager (VxVM) and other software still ruled the enterprise world.
When Sun added ZFS to Solaris, they did not get rid of UFS and/or SVM, nor prevent Veritas from being installed. When FreeBSD added ZFS, they did not get rid of UFS or GEOM either.
If an admin wanted or wants (or needs) to use the 'old' way of doing things they can.
It may be a good thing, and it may not. Linux has a bajillion file systems, some more useful than others, and that is unique in some ways.
Solaris and other enterprise-y Unixes at the time only had one. Even the BSDs generally only have a few that they run on instead of ext2/3/4, XFS, ReiserFS (remember when that was going to take over?), btrfs, bcachefs, etc, etc, etc.
At most, a company may have purchased a license for Veritas:
* https://en.wikipedia.org/wiki/Veritas_Storage_Foundation
By rolling everything together, you get ACID writes, atomic space-efficient low-overhead snapshots, storage pools, etc. All this just be removing one layer of indirection and doing some telescoping:
* https://blogs.oracle.com/bonwick/rampant-layering-violation
It's not "modularity bad", but that to achieve the same result someone would have had to write/expand a layer-to-layer API to achieve the same results, and no one did. Also, as a first-order estimate of complexity: how many lines of code (LoC) are there in mdraid/LVM/ext4 versus ZFS (or UFS+SVM on Solaris).
What would you recommend over zfs for small-scale storage servers? XFS with mdraid?
I'd also love to hear your opinion on the Reiser5 paper.
That's problem only with RAID1, only when copies=2 (granted, most often used case) and only when the underlying device cannot report which sector has gone bad.
There are valid reasons, most having to do with filesystem usage and optimization. Off the top of my head:
- more efficient re-syncs after failure (don't need to re-sync every block, only the blocks that were in use on the failed disk)
- can reconstruct data not only on disk self-reporting, but also on filesystem metadata errors (CRC errors, inconsistent dentries)
- different RAID profiles for different parts of the filesystem (think: parity raid for large files, raid10 for database files, no raid for tmp, N raid1 copies for filesystem metadata)
and for filesystem encryption:
- CBC ciphers have a common weakness: the block size is constant. If you use FS-object encryption instead of whole-FS encryption, the block size, offset and even the encryption keys can be varied across the disk.
Volume management is a just a hack. We had all of these single-disk filesystems, but single disks were too small. So volume management was invented to present the illusion (in other words, lie) that they were still on single disks.
If you replace "disk" with "DIMM", it's immediately obvious that volume management is ridiculous. When you add a DIMM to a machine, it just works. There's no volume management for DIMMs.
Storage is at the bottom of the caching hierarchy where people get inventive to avoid rebuilding. Rebuilding would be really costly there. Hence we use volume management to spare us the cost of rebuilding.
RAM also tends to have uniform performance. Which is not true for disk storage. So while you don't usually want to control data placement in RAM, you very much want to control what data goes on what disk. So the analogy confuses concepts rather than illuminating commonalities.
One of the creators of ZFS, Jess Bonwick, explained it in 2007:
> While designing ZFS we observed that the standard layering of the storage stack induces a surprising amount of unnecessary complexity and duplicated logic. We found that by refactoring the problem a bit -- that is, changing where the boundaries are between layers -- we could make the whole thing much simpler.
* https://blogs.oracle.com/bonwick/rampant-layering-violation
RAIDZ is part of the VDEV (Virtual Device) layer. Layered on top of this is the ZIO (ZFS I/O layer). Together, these form the SPA (Storage Pool Allocator).
On top of this layer we have the ARC, L2ARC and ZIL. (Adaptive Replacement Caches and ZFS Intent Log).
Then on top of this layer we have the DMU (Data Management Unit), and then on top of that we have the DSL (Dataset and Snapshot Layer). Together, the SPA and DSL layers implement the Meta-Object Set layer, which in turn provides the Object Set layer. These implement the primitives for building a filesystem and the various file types it can store (directories, files, symlinks, devices etc.) along with the ZPL and ZAP layers (ZFS POSIX Layer and ZFS Attribute Processor), which hook into the VFS.
ZFS isn't just a filesystem. It contains as many, if not more, levels of layering than any RAID and volume management setup composed of separate parts like mdraid+LVM or similar, but much better integrated with each other.
It can also store stuff that isn't a filesystem. ZVOLs are fixed size storage presented as block devices. You could potentially write additional storage facilities yourself as extensions, e.g. an object storage layer.
Which was precisely Sun/Oracle's goal when they released ZFS under the purposefully GPL incompatible CDDL. Sun was hoping to make OpenSolaris the next Linux whilst ensuring that no code from OpenSolaris could be moved back to linux. I can't think of another plausible reason why they would write a new open source license for their open source operating system and making such a license incompatible with the GPL.
Some people argue that Sun (or the Sun engineer) as creator of the license made the CDDL intentionally GPL incompatible.[13] According to Danese Cooper one of the reasons for basing the CDDL on the Mozilla license was that the Mozilla license is GPL-incompatible. Cooper stated, at the 6th annual Debian conference, that the engineers who had written the Solaris kernel requested that the license of OpenSolaris be GPL-incompatible.[18]
Mozilla was selected partially because it is GPL incompatible. That was part
of the design when they released OpenSolaris. ... the engineers who wrote Solaris
... had some biases about how it should be released, and you have to respect that.> Simon Phipps (Sun's Chief Open Source Officer at the time), who had introduced Cooper as "the one who actually wrote the CDDL",[19] did not immediately comment, but later in the same video, he says, referring back to the license issue, "I actually disagree with Danese to some degree",[20] while describing the strong preference among the engineers who wrote the code for a BSD-like license, which was in conflict with Sun's preference for something copyleft, and that waiting for legal clearance to release some parts of the code under the then unreleased GNU GPL v3 would have taken several years, and would probably also have involved mass resignations from engineers (unhappy with either the delay, the GPL, or both—this is not clear from the video). Later, in September 2006, Phipps rejected Cooper's assertion in even stronger terms.[21]
So of the available licenses at the time, Engineering wanted BSD and Legal wanted GPLv3, so the compromise was CDDL.
Edit: Nevermind, debunked by Bryan Cantrill. It was to allow for proprietary drivers.
> Simon Phipps (Sun's Chief Open Source Officer at the time), who had introduced Cooper as "the one who actually wrote the CDDL",[19] did not immediately comment, but later in the same video, he says, referring back to the license issue, "I actually disagree with Danese to some degree",[20] while describing the strong preference among the engineers who wrote the code for a BSD-like license, which was in conflict with Sun's preference for something copyleft, and that waiting for legal clearance to release some parts of the code under the then unreleased GNU GPL v3 would have taken several years, and would probably also have involved mass resignations from engineers (unhappy with either the delay, the GPL, or both—this is not clear from the video). Later, in September 2006, Phipps rejected Cooper's assertion in even stronger terms.[21]
* https://en.wikipedia.org/wiki/Common_Development_and_Distrib...
So of the available licenses at the time, Engineering wanted BSD and Legal wanted (to wait for) GPLv3, so the compromise was CDDL.
Lovely except it really was decided to explicitly make OpenSolaris incompatible with GPL. That was one of the design points of the CDDL. I was in that room, Bryan and you were not, but I know its fun to re-write history to suit your current politics. I pleaded with Sun to use a BSD family license or the GPL itself and they would consider neither because that would have allowed D-Trace to end up in Linux. You can claim otherwise all you want...this was the truth in 2005.
(In many ways, it still is a time of pirates, we just moved a bit higher in the stack...)
I wouldn't say McNealy was that different than any of those, though others like Joy and Bechtolsheim had a more salutary influence. To the extent that there was any overall difference, it seemed small. Working on protocol interop with DEC products and Sun products was no different at all. Sun went less-commodity with SPARC and SBus, they got in bed with AT&T to make their version of UNIX seem more standard than competitors' even though it was more "unique" in many ways, there were the licensing games, etc. Better than Oracle, yeah, but I wouldn't go too much further than that.
For (the lack of) openness, I agree, but the claim that they were not innovative needs stronger evidence.
The whole open-source steer by SUN was a very disingenous strategy, forced by the changed landscape in order to try and salvage some parvence of relevance. Most people saw right through it, which is why SUN ended up as it did shortly thereafter: broke, acquired, and dismantled.
> Simon Phipps (Sun's Chief Open Source Officer at the time), who had introduced Cooper as "the one who actually wrote the CDDL",[19] did not immediately comment, but later in the same video, he says, referring back to the license issue, "I actually disagree with Danese to some degree",[20] while describing the strong preference among the engineers who wrote the code for a BSD-like license, which was in conflict with Sun's preference for something copyleft, and that waiting for legal clearance to release some parts of the code under the then unreleased GNU GPL v3 would have taken several years, and would probably also have involved mass resignations from engineers (unhappy with either the delay, the GPL, or both—this is not clear from the video). Later, in September 2006, Phipps rejected Cooper's assertion in even stronger terms.[21]
So of the available licenses at the time, Engineering wanted BSD and Legal wanted GPLv3, so the compromise was CDDL.
I am willing to bet that Google had the same thought. And I am also willing to bet that Google is regretting that thought now.
That last one is likely to get some kind of hacky workaround. But nobody wants to do the invasive changes necessary for actual BPR to enable that entire list.
Unless you are living in 2012 on a RHEL/CENTOS 6/7 machine, btrfs has been stable for way too long. I have been using btrfs as the sole filesystem on my laptop in standard mode, on my desktop as RAID0 and my NAS as RAID1 for more that two years. I have experienced absolutely zero data loss. Infact, btrfs recovered my laptop and desktop from broken package updates many times.
You might have had some issues when you tried btrfs on distros like RHEL that did not backport the patches to their stable versions because they don't support btrfs commercially. Try something like openSUSE that backports btrfs patches to stable versions or use something like arch.
> That's true, however, the amount is breakage is no different from any other out-of-tree module, and it unlikely to happen with a patch version of a working kernel (in fact, it happen with the 5.0 release).
This is a filesystem that we are talking. In no circumstances will any self respecting sysadmin use a file system that has even a small change of breaking with a system update.
Meanwhile ZFS has survived disk failures, removing 2 disks from an 8 disk RAIDZ3 array and then putting them back, random SATA interface connection issues that were resolved by reseating the HDD, and will probably survive anything else that I throw at it.
RAIZ/Z2 avoids the issue by having slightly different semantics. That's why it is Z/Z2, not 5/6.
VMWare Fusion, on the other hand, powers the desktop environment I've used as a daily work machine for the last 6 months, and I've had absolutely zero problems other than trackpad scrolling getting emulated as mouse wheel events (making pixel-perfect scroll impossible).
Despite that one annoyance, it's definitely worth paying for if you're using it for any serious or professional purpose.
VirtualBox itself is GPL. There is no lawsuit risk.
What requires "commercial considerations" is the extension pack.
The extension pack is required for:
> USB 2.0 and USB 3.0 devices, VirtualBox RDP, disk encryption, NVMe and PXE boot for Intel cards
If licensing needs to be considered (ie. in a corporate environment), but one doesn't need the functionalities above, then there's no issue.
It might be, but let's just say that Oracle aren't big fans of $WORK, and our founders are big fans of them. Thus our legal department are rather tetchy about anything that could give them even the slightest chance of doing anything.
> What requires "commercial considerations" is the extension pack.
And our legal department are nervous about that being installed, even by accident, so they prefer to minimise the possibility.
Is the expectation here that firms offering software under non-commercial-use-is-free licenses just run it entirely on the honour system? And isn't it true that many firms use unlicensed software, hence the need for audits?
They can also apply stronger heuristics, like popping up a dialogue box if the computer is centrally-managed (e.g.: Mac MDM, Windows domain, Windows Pro/Enterprise, etc.).
The (commercially licensed) Extensions pack provide "Support for USB 2.0 and USB 3.0 devices, VirtualBox RDP, disk encryption, NVMe and PXE boot for Intel cards"[1] and some other functionality e.g. webcam passthrough [2]. There may be additional functionality enabled by the Extension pack I cannot find at a glance, but those are the main things.
[1] https://www.virtualbox.org/wiki/Downloads [2] https://www.virtualbox.org/manual/ch01.html#intro-installing
With my MBP as host and Ubuntu as guest, I found that VirtualBox (with and without guest extensions installed) had a lot of graphical performance issues that Fusion did not.
I don't think it has to be conceivable with Oracle...
Unfortunately I have to agree with Linus on this one. Messing with Oracle's stuff is dangerous if you can't afford a comparable legal team.
Money. Anecdotally that's the primary reason Oracle do anything.
I worked for a tiny startup (>2 devs full time) where Oracle tried to extract money from us because we used MariaDB on AWS.
If you think this sounds ridiculous you probably got it right.
(Why? Because someone inexperienced with Oracle had filled out the form while downloading the mySQL client.)
Don't be so sure about this.
However the person he is replying to was not actually asking to have ZFS included in the mainline kernel. As noted above, that could never happen, and I believe that Linus is only bringing it up to deflect from the real issue. What they were actually asking is for Linux to revert a change that was made for no other reason than to hinder the use of ZFS.
Linux includes a system which restricts what APIs are available to each module based on the license of the module. GPL modules get the full set of APIs whereas non-GPL modules get a reduced set. This is done strictly for political reasons and has no known legal basis as far as I'm aware.
Not too long ago a change was made to reduce the visibility of a certain API required by ZFS so only GPL modules could use it. It's not clear why the change was made, but it was certainly not to improve the functionality of the kernel in any way. So the only plausible explanation to me is that it was done just to hinder the use of ZFS with Linux, which has been a hot political issue for some time now.
Saving and restoring registers is an astoundingly generic function. If you list all the kernel exports and sort by how much they make your work derivative, it should be near the very bottom.
It was always frowned upon:
> In other words: it's still very much a special case, and if the question was "can I just use FP in the kernel" then the answer is still a resounding NO, since other architectures may not support it AT ALL.
> Linus Torvalds, 2003
and these specific functions, that were marked as GPL were already deprecated for well over a decade.
> It was always frowned upon
Whether it's frowned upon is a completely different issue from whether it intertwines your data so deeply with the kernel that it makes your code a derivative work subject to the GPL license. Which it doesn't.
> if the question was "can I just use FP in the kernel" then the answer is still a resounding NO, since other architectures may not support it AT ALL.
It's not actually using floating point, it's using faster instructions for integer math, and it has a perfectly viable fallback for architectures that don't have those instructions. But why use the slower version when there's no real reason to?
> and these specific functions, that were marked as GPL were already deprecated for well over a decade.
But the GPL export is still there, isn't it? It's not that functionality is being removed, it's that functionality is being shifted to only have a GPL export with no license-based justification for doing so.
He is not going to beg people outside kernel, whether he is allowed to change something that may break their module. On the contrary, they must live with any breackage that is thrown at them.
Again, that symbol was deprecated for well over a decade. How long does it take to be allowed to remove it?
> Again, that symbol was deprecated for well over a decade.
But not the GPL equivalent of the symbol. That symbol is not deprecated.
One can interpret this as something legally significant, or an embarrassing private anecdote, or nothing substantial at all, maybe even just talk. However, I'd give them the benefit of the doubt. Not the least since they could be the ones against Oracle's legal dept...
If you don’t like that don’t use it.
let me stop you right there. This being "Oracle," and its litigious nature, how can you truly be aware or sure?
Linus is literally saying there is a legal basis.
The functionality I'm describing has absolutely nothing to do with ZFS or Oracle in any way. If you really think the reach of Oracle is so great, then why not block all Oracle code from ever running on the OS? That seems to me to be just as justified as this change.
...to be fair, I would probably run that module.
I can't make a informed opinion but my uninformed gut feeling is oracle have done what they are suing google for having done.
CoW filesystems do trade performance for data safety. Or did you mean there are other _stable/production_ CoW filesystems with better performance? If so, please do point them out!
Just ask yourself what happens when a thin pool runs out of actual, physical disk blocks?
I have actually managed to run out of blocks on XFS on thin LV and it's an interesting experience. XFS always survoved just fine, but some files basically vanished. Looks like mostly those that were open and being written to at exhaustion time, like for example a mariadb database backing store. Files that were just sitting there were perfectly fine as far as I could tell.
Still, you definitely should never put data on a volume where a pool can be exhausted, without a backup as I don't think there is really a bulletproof way for a filesystem to handle that happening suddenly.
ZFS doesn't over-provision anything by default. The only case I'm aware of where you can over-provision with ZFS is when you explicitly choose to thin provision zvols (virtual block devices with a fixed size). This can't be done with regular file systems which grow as needed, though you can reserve space for them.
File systems do handle running out of space (for a loose definition of handle) but they never expect the underlying block device to run out of space, which is what happens with over-provisioning. That's a problem common to any volume manager that allows you to over provision.
With ZFS, if I take a snapshot and then delete 10GB of data my file system will appear to have shrunk by 10GB. If I compare the output of df before and after deleting the data, df will tell me that "size" and "used" have decreased by 10GB while "available" remained constant. Once the snapshot is deleted that 10GB will be made available again and the "size" and "available" columns in df will increase. It avoids over-provisioning by never promising more available space than it can guarantee you're able to write.
I think you're trying to relate ZFS too much to how LVM works, where LVM is just a volume manager that exposes virtual devices. The analogue to thin provisioned LVM volumes is thin-provisioned zvols, not regular ZFS file systems. I can choose to use ZFS in place of LVM as a volume manager with XFS as my file system. Over-provisioned zvols+XFS will have functionally equivalent problems as over-provisioned LVM+XFS.
ZFS has quotas and reservations. The former is a maximum allocation for a dataset. The latter is a minimum guaranteed allocation. Neither actually allocate blocks from the pool. These don't relate in any comparable way to how LVM works. They are just numbers to check when allocating blocks.
If I have a 10GB pool and I create 10 empty file systems, the sizes reported in df will be 100GB. It's not quite a lie either, because each of those 10 file systems does in fact have 10GB of space available I could write 10GB to any one of them. If I write 1GB to one of those file systems, the "size" and "available" spaces for the other nine will all shrink despite not having a single byte of data written to them.
With ZFS and df the "size" column is really only measuring the maximum possible size (at this point in time, assuming nothing else is written) so it isn't very meaningful, but the "used" and "available" columns do measure something useful.
You could build a pool-aware version of DF that reflects this, by grouping file systems in a pool together and reporting that the pool has 10GB available. But frankly there's not enough benefit to doing that because people with storage pools already understand summing up all the available space from df's output is not meaningful. Tools like zpool list and BTRFS's df equivalent already correctly report the total free space in the pool.
Supporting reflinks is actually more, than can be said about ZoL (see zfsonlinux#405).
No. Distributing (ie. precompiled distro with ZFS) will. You are free to run any software on your machine as you so desire.
- The kernel team may break it at any time, and won't care if they do.
- It doesn't seem to be well-maintained.
- Performance is not that great compared to the alternatives.
- Using it opens you up to the threat of lawsuits from Oracle. Given history, this is a real threat. (This is one that should be high for Linus but not for me - there is no conceivable reason that Oracle would want to threaten me with a lawsuit.)