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ZFS On Linux Runs Into A Snag With Linux 5.0

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  • Originally posted by pal666 View Post
    only zfs has such deficiency. btrfs can have multiple copies of data on one drive. and it has multiplie copies of metadata on one drive by default. btrfs is superior to zfs in any way possible
    This comment demonstrates you have no idea what you're talking about. A vdev can be a disk partition; so partition your disk into two vdevs and mirror them. Or you can just use the built in fs features:
    https://docs.oracle.com/cd/E19253-01...vpg/index.html

    In particular, disks are cheap, I never put anything, no matter how trivial, on a single disk without redundancy any more. The fact that you're talking about this raises questions. I guess maybe you're in Burundi, working with a budget of $2, or something?

    And of course you can use ZFS on a single disk, there's just no point in doing so. https://forums.freenas.org/index.php...ive-zfs.35515/

    From your comments it appears that you're a btrfs fan, and are using this in a professional situation? I'd be happy to switch to Btrfs, but can't find any storage admin willing to endorse such a thing. Everyone (but you) views Btrfs as too unstable for serious production use, and things like this don't help:

    https://www.phoronix.com/scan.php?pa...RAID-56-Is-Bad
    https://www.phoronix.com/scan.php?pa...-Not-All-Clear
    https://superuser.com/questions/1371...hile-balancing
    https://btrfs.wiki.kernel.org/index.php/RAID56
    https://www.reddit.com/r/btrfs/comme..._raid_56_bugs/
    https://news.ycombinator.com/item?id=16798157
    Last edited by pgoetz; 01-13-2019, 11:55 AM.

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    • Originally posted by pal666 View Post
      no, btrfs was started by one guy before he went to work for oracle. iirc he was working for suse.
      so what is stopping oracle from contributing zfs propely just as they "contributed" btrfs?
      Yeah, that's wrong too. Btrfs started at Oracle: https://www.linuxfoundation.org/blog...ason-on-btrfs/

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      • Originally posted by k1e0x View Post

        OpenZFS is a fork and it's *not* a corporate filesystem project. They have ZERO involvement with Oracle. It's license is similar to MPL (are you reading this in Firefox, it's MPL too) and one could argue it's more permissive and free than Linux itself. (hence it's inclusion in FreeBSD, Mac OSX, even Microsoft Windows now. The only place it's "not allowed" is Linux.)

        My problem isn't the API change. I'm sure they will work that out. The issue is the emotional comments by Linux kernel dev's and the users.. whatever Sun's motivation. (and someone show me some proof they actually believed CDDL was not compatible, because it's was Debian that made that determination.) ..Whatever their motivation.. they are long since dead. Time to move on.

        IMO this is dumb. NIH and zealots a lot. You have two pieces of awesome totally open source technology Linux and ZFS, make them work together and put *actual* commercial storage (cough NetApp) out of business. Technology and solutions to problems should not be based on how you feel about Sun.
        Firefox doesn't require an out of tree module to function. For the CDDL code to be link-compatible with GPL 2+ code, you'd need a separate royalty-free perpetual patent grant to all GPL licensees, or be sure that all patents have expired. Not impossible, but without Oracle on board, it'd be 2033 at the earliest.

        The CDDL is at first glance, incompatible with the "without any other restriction" clause of the GPL. Nobody with deep pockets is going to risk distributing a compiled ZFS module for fear that a Linux rights-holder will be after them, either for a paycheck or for business/competition reasons.

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        • Originally posted by oiaohm View Post
          SIMD has to have the same protection switches as using FPU. Thank you intel for deciding to recycle some the less stable register copy operations in side their cpus..

          The Linux kernel has a crypto_shash that wraps over all you hardware acceleration for checksums. Really bad news to use a lot of the hardware accelerations you need patent licenses Guess what OIN has got those patents license for the Linux kernel. Wait for the other shoe to drop. The patent license that OIN aquired only cover you if your code is GPL.

          On hardware with proper checksum hardware accelerators ZFS on Linux not being GPL is going to be slow vs GPL file-systems in the Linux kernel doing checksums.

          This is one of the problems you hit when you go to freebsd from linux is that hardware accelerators no longer have drivers and it not possible to write a non GPL driver for them.
          Why wouldn't the use of accelerators be covered under the patent exaushtion doctrine? What patents exactly are we talking about?

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          • Originally posted by oiaohm View Post
            https://yarchive.net/comp/linux/kernel_fp.html
            This is when __kernel_fpu_begin and __kernel_fpu_end features were introduced into the Linux kernel.
            ...
            The reality here like it or not the ZFS On Linux are at fault.
            ...
            That was a very interesting comment, and I apologize for editing it. Just want to comment on two things.
            1) Nobody is really at fault here, it just so happens that the ZFS kernel driver code for x86 and x86_64 was using the decades old x87 FPU and so required access to the FPU registers directly. It's a software development accident. Things like that happen all the time. Unfortunately people on the LKML tend to get a little bit nervous quite often.
            2) Since ZOL also compiles for the arm, aarch64, ppc64 and ppc architectures, there is probably a solution or workaround that does not involve accessing the x87 registers directly. So yes, in the end the burden of fixing this will be on ZOL developers, but there is probably a simple solution, and the ZOL code will only improve from not messing with the (particularly finicky) x87 registers directly. So in the end ZFS on Linux users will benefit from this.

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            • Originally posted by pdffs View Post
              It's a shame that BTRFS turned out to be be such a steaming pile of crap
              Let's disagree on such a bold but totally unbacked statement. Works for me and NOT plagued by troubles like out of tree modules do.

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              • Originally posted by pgoetz View Post
                In particular, disks are cheap, I never put anything, no matter how trivial, on a single disk without redundancy any more. The fact that you're talking about this raises questions. I guess maybe you're in Burundi, working with a budget of $2, or something?
                Disks are cheap, blah-doh. But, say my laptop just lacks space to add yet another drive, not to mention power consumption and weight. Somehow btrfs can live with just one drive - storing metadata (or even data, if desired) using DUP storage scheme. That is, written twice to same disk. Somehow it helps vs occasional bad sector or other "small-scale" upsets like this, avoiding massive damage in this case.

                On other hand ZFS implies high-profile enterprise HW setup and wouldn't do reasonably if it somthing else than that. Btrfs also got very decent tesing coverage when Facebook deployed it on their servers. Sure, not all features, just subset of these. I strongly doubt ZoL gets anyhow comparable testing coverage at all.

                p.s. and if someone is not happy with Linux licensing, okay, nobody forces you to use Linux, isn't it?
                Last edited by SystemCrasher; 01-13-2019, 02:47 PM.

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                • Originally posted by AndrewDB View Post

                  That was a very interesting comment, and I apologize for editing it. Just want to comment on two things.
                  1) Nobody is really at fault here, it just so happens that the ZFS kernel driver code for x86 and x86_64 was using the decades old x87 FPU and so required access to the FPU registers directly. It's a software development accident. Things like that happen all the time. Unfortunately people on the LKML tend to get a little bit nervous quite often.

                  2) Since ZOL also compiles for the arm, aarch64, ppc64 and ppc architectures, there is probably a solution or workaround that does not involve accessing the x87 registers directly. So yes, in the end the burden of fixing this will be on ZOL developers, but there is probably a simple solution, and the ZOL code will only improve from not messing with the (particularly finicky) x87 registers directly. So in the end ZFS on Linux users will benefit from this.
                  1. No it was accessing some SIMD instructions, which for some reason Intel put behind the same initialization interface/registers, to accelerate checksum calculations.

                  2. Likely with a performance penalty or having to go to GPL earmarked crypto interfaces.

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                  • Originally posted by SystemCrasher View Post
                    Disks are cheap, blah-doh. (1)But, say my laptop just lacks space to add yet another drive, not to mention power consumption and weight. (2)Somehow btrfs can live with just one drive - storing metadata (or even data, if desired) using DUP storage scheme. That is, written twice to same disk. Somehow it helps vs occasional bad sector or other "small-scale" upsets like this, avoiding massive damage in this case.

                    (3)On other hand ZFS implies high-profile enterprise HW setup and wouldn't do reasonably if it somthing else than that. Btrfs also got very decent tesing coverage when Facebook deployed it on their servers. Sure, not all features, just subset of these. I strongly doubt ZoL gets anyhow comparable testing coverage at all.

                    p.s. and if someone is not happy with Linux licensing, okay, nobody forces you to use Linux, isn't it?
                    (1)First of all, get yourself decent laptop. Another M2 slot and drive means just marginal increase in weight or power usage. Some models even have 4 of these slots (MSI GT80). I am not telling you that you have to buy that particular machine, just that machines with optional multiple drives do exist. Lots of choices if it comes to just 1-2 extra M2 slots.
                    At the moment you bring forth argument "I was stupid to buy single drive laptop and I am smart to use btrfs because it would compensate my stupidity".

                    (2) Ehm, you really-really think ZFS is limited here? zfs set copies=2 dataset OR use 2 mirrored ZFS partitions on a single drive OR combine the two. Or increase the number of copies. OR do everything mentioned and have absurd amount of copies.

                    BTRfs is actually more vulnerable of the two, because it's using crc32c hash trees and makes AFAIK only 2 copies of metadata. ZFS uses Merkle hash trees and spreads it's metadata around. When you go fully paranoiac you can configure it to be resistant to hundreds of bad sectors. Your drive would probably die long before you get to worry about it, and when your drive suddenly tucks it's tail under it's head and says "good night", no file system can help you.

                    (3) You claim that ZFS implies "high-profile enterprise HW setup and wouldn't do reasonably it it was 'somthing' else than that" And then bring us example of btrfs enterprise usage? What was the flippin' point of your previous sentence then?. Anyway, bullshit again. I've used ZFS on Asus eeePC netbook, turning off fancy features and I am using ZFS on 2-drive mirror in my current Dell laptop. And in my i7 gaming PC. And it does not have issues of space congestion or fragmentation.

                    I got a laugh looking at https://btrfs.wiki.kernel.org/index....trfs_stable.3F
                    Is btrfs stable?
                    Short answer: Maybe.
                    Last edited by aht0; 01-14-2019, 04:49 AM.

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                    • ZFS mirrors (0.8.0+) with native encryption runs very well with linux-hardened & is better suited to running vm images than BTRFS.

                      BTRFS on LUKS makes a great root filesystem

                      Use the right tools for each use case

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