Re: btrfs problems on new file system

[covici@ccs.covici.com]

Chris Murphy <lists@colorremedies.com> wrote:

> On Sat, Dec 26, 2015 at 12:22 PM,  <covici@ccs.covici.com> wrote:
> > Chris Murphy <lists@colorremedies.com> wrote:
> >
> >> On Sat, Dec 26, 2015 at 4:38 AM,  <covici@ccs.covici.com> wrote:
> >> > Duncan <1i5t5.duncan@cox.net> wrote:
> >> >
> >> >> covici posted on Sat, 26 Dec 2015 02:29:11 -0500 as excerpted:
> >> >>
> >> >> > Chris Murphy <lists@colorremedies.com> wrote:
> >> >> >
> >> >> >> If you can post the entire dmesg somewhere that'd be useful. MUAs tend
> >> >> >> to wrap that text and make it unreadable on list. I think the problems
> >> >> >> with your volume happened before the messages, but it's hard to say.
> >> >> >> Also, a generation of nearly 5000 is not that new?
> >> >> >
> >> >> > The file system was only a few days old.  It was on an lvm volume group
> >> >> > which consisted of two ssd drives, so I am not sure what you are saying
> >> >> > about lvm cache -- how could I do anything different?
> >> >> >
> >> >> >> On another thread someone said you probably need to specify the device
> >> >> >> to mount when using Btrfs and lvmcache? And the device to specify is
> >> >> >> the combined HDD+SSD logical device, for lvmcache that's the "cache
> >> >> >> LV", which is the OriginLV + CachePoolLV. If Btrfs decides to mount the
> >> >> >> origin, it can result in corruption.
> >> >> >
> >> >> > See above.
> >> >>
> >> >> I think he mixed up two threads and thought you were running lvm-cache,
> >> >> not just regular lvm, which should be good unless you're exposing lvm
> >> >> snapshots and thus letting btrfs see multiple supposed UUIDs that aren't
> >> >> actually universal.  Since btrfs is multi-device and uses the UUID to
> >> >> track which devices belong to it (because they're _supposed_ to be
> >> >> universally unique, it's even in the _name_!), if it sees the same UUID
> >> >> it'll consider it part of the same filesystem, thus potentially causing
> >> >> corruption if it's a snapshot or something that's not actually supposed
> >> >> to be part of the (current) filesystem.
> >> >
> >> > I found a few more log entries, perhaps these may be helpful to track
> >> > this down, or maybe prevent the filesystem from going read-only.
> >>
> >> No, you need to post the entire dmesg. The "cut here" part is maybe
> >> useful for a developer diagnosing Btrfs's response to the problem, but
> >> the problem, or the pre-problem, happened before this.
> >
> > It would be a 20meg file, if I were to post the whole file.  but I can
> > tell you, no hardware errors at any time.
> 
> The kernel is tainted, looks like a proprietary kernel module, so you
> have to have very good familiarity with the workings of that module to
> know whether it might affect what's going on, or you'd have to retest
> without that kernel module.
> 
> Anyway, asking for the whole dmesg isn't arbitrary, it saves times
> having to ask for more later. The two things you've provided so far
> aren't enough, any number of problems could result in those messages.
> So my suggestion is when people ask for something, provide it or don't
> provide it, but don't complain about what they're asking for. The
> output from btrfs-debug-tree might be several hundred MB. The output
> from btrfs-image might be several GB. So if you're not willing to
> provide 100kB, let alone 20MB, of kernel messages that might give some
> hint what's going on, the resistance itself is off putting. It's like
> having to pull your own loose tooth for you, no one really wants to do
> that.

How far back do you want to go in terms of the messages?


-- 
Your life is like a penny.  You're going to lose it.  The question is:
How do
you spend it?

         John Covici
         covici@ccs.covici.com