Date: Mon, 1 Jul 2013 10:04:22 -0700 From: Jeremy Chadwick <jdc@koitsu.org> To: Paul Mather <pmather@vt.edu> Cc: freebsd-stable List <freebsd-stable@freebsd.org>, Scott Sipe <cscotts@gmail.com> Subject: Re: ZFS Panic after freebsd-update Message-ID: <20130701170422.GA65858@icarus.home.lan> In-Reply-To: <C13462A8-88DC-4EEF-9356-CF655B8EA8E8@vt.edu> References: <CA%2B30O_P7=3FanLaxjHQ71grqWLfTxNJXb6kP5-eWYWEYZFoVtw@mail.gmail.com> <20130701154925.GA64899@icarus.home.lan> <C13462A8-88DC-4EEF-9356-CF655B8EA8E8@vt.edu>
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On Mon, Jul 01, 2013 at 12:23:45PM -0400, Paul Mather wrote: > On Jul 1, 2013, at 11:49 AM, Jeremy Chadwick <jdc@koitsu.org> wrote: > > > On Mon, Jul 01, 2013 at 11:35:30AM -0400, Scott Sipe wrote: > >> *** Sorry for partial first message! (gmail sent after multiple returns > >> apparently?) *** > >> > >> Hello, > >> > >> I have not had much time to research this problem yet, so please let me > >> know what further information I might be able to provide. > >> [[...]] > >> Any thoughts? > > > > Thoughts: > > > > [[..]] > > Of course when I see lines like this: > > > > Trying to mount root from zfs:zroot > > > > ...this greatly diminishes any chances of "live debugging" on the > > system. It amazes me how often I see this come up on the lists -- people > > who have ZFS problems but use ZFS for their root/var/tmp/usr. I wish > > that behaviour would stop, as it makes debugging ZFS a serious PITA. > > This comes up on the list almost constantly, sad panda. > > > I'm not sure why it amazes you that people are making widespread use of ZFS. It's not widespread use of ZFS. It's widespread use of ZFS as their sole filesystem (specifically root/var/tmp/usr, or more specifically just root/usr). People are operating with the belief that "ZFS just works", when reality shows "it works until it doesn't". The mentality seems to be "it's so rock solid it'll never break" along with "it can't happen to me". I tend to err on the side of caution, hence avoidance of ZFS for critical things like the aforementioned. It's different if you have a UFS root/var/tmp/usr and ZFS for everything else. You then have a system you can boot/use without issue even if ZFS is crapping the bed. > You could make the same argument that people shouldn't use UFS2 > journaling on their file systems because bugs in the implementation > might make debugging journaled UFS2 file systems "a serious PITA." Yup, and I do make that argument, quite regularly at that. There is even some evidence at this point in time that softupdates are broken: http://lists.freebsd.org/pipermail/freebsd-fs/2013-June/017424.html > The point is that there are VERY compelling reasons why people might > want to use ZFS for root/var/tmp/usr/etc. (pooled storage; easy > snapshots; etc.) and there should come a time when a given file system > is "generally regarded as safe." While there may be compelling reasons, those reasons quickly get shot down when they realise they have a system they can't easily do troubleshooting with when the issue is with ZFS. > I'd say the time for ZFS came when they removed the big disclaimer > from the boot messages. If ZFS is dangerous, they should reinstate > the "not ready for production" warning. Until they do, I think it's > unfair to castigate people for using ZFS universally. The warning meant absolutely nothing at the time (it did not keep people away from it), and would mean nothing now if brought back. A single kernel printf() is not the right choice of action. Are we better off today than we were when ZFS was originally ported over? Yes, by far. Lots of improvements, in many great/good ways. No argument there. But there is no way I'd risk putting my root filesystem (or other key filesystems) on it -- still too new, still too many bugs, and users don't know about those problems until it's too late. > Isn't it a recurring theme on freebsd-current and freebsd-stable that > more people need to use features so they can be debugged in realistic > environments? If you're telling them, "don't use that because it > makes debugging harder," how are they supposed to get debugged and > hence improved? :-) 95% of FreeBSD users cannot debug kernel problems**. To debug a kernel problem, you need: a crash dump, a usable system with the exact kernel/world where the crash happened (i.e. you cannot crash 8.4 ZFS and boot into 8.2 and reliably debug it using that), and (most important of all) a developer who is familiar with kernel debugging *and* familiar with the bits which are crashing. Those who say what you're quoting are often the latter. Part of the "need people to try this" process you refer to is what stable/X is about, *without* the extra chaos of head. I'm one of those who for the past 15 years has advocated stable/X usage for a lot of reasons; I'll save the diatribe for some other time. But the OP is running -RELEASE, and chooses to run that, along with use of freebsd-update for binary updates. Their choices are limited: stick with 8.2, switch to stable/X, cease use of ZFS, or change OSes entirely. But even stable/X doesn't provide enough coverage at times (the recent fxp(4)/dhclient issue is proof of that). It's just too bad so many people have this broken mindset of what "stability" means on FreeBSD. ** = This number is probably more like 99%, especially when you consider what FreeNAS is catering to/trying to accomplish. -- | Jeremy Chadwick jdc@koitsu.org | | UNIX Systems Administrator http://jdc.koitsu.org/ | | Making life hard for others since 1977. PGP 4BD6C0CB |
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