The image doesn't have a valid superblock. I'm really confused as to how that could've happened.
On Fri, Aug 18, 2017 at 7:21 PM, Qu Wenruo <quwenruo.bt...@gmx.com> wrote: > > > On 2017年08月19日 05:52, Zirconium Hacker wrote: >> >> Ok, so since it's clear now that I need that 5 GB device to be >> present... I found the image file. But how do I get BTRFS to >> recognize the image as a device? > > > # losetup -f > Remember the loop*, here use /dev/loop1 as example. > > # losetup /dev/loop1 <your image> > # partprobe /dev/loop1 > Then you should have /dev/loop1p1 > > # btrfs dev rescan > If nothing wrong happened, you should be good to go. > > Thanks, > Qu > > >> I have zero experience with >> multi-device systems. Setting it up as a loop device doesn't fix >> mounting, and wipefs doesn't detect the BTRFS magic number, but >> printing some of it to console shows it does have real data. Writing >> the magic number onto it (it's a copy of the original to be safe) >> shows in dump-super, but all other values are zero. >> >> I tried sending the above on my phone earlier but it was detected as a >> "virus" because it contained HTML. Whoops. >> >> On Fri, Aug 18, 2017 at 11:00 AM, Chris Murphy <li...@colorremedies.com> >> wrote: >>> >>> On Fri, Aug 18, 2017 at 2:47 AM, Zirconium Hacker <jared.e...@gmail.com> >>> wrote: >>> >>>> I vaguely remember following this guide at some point: >>>> >>>> http://marc.merlins.org/perso/btrfs/post_2014-05-04_Fixing-Btrfs-Filesystem-Full-Problems.html >>>> -- specifically the "Balance cannot run because the filesystem is >>>> full" part. This may have broken some things? >>>> >>> >>> If you don't do 'btrfs device delete /dev/loop0' or if that command >>> does not complete, then it's possible to get into the situation you're >>> in. >>> >>> Have you ever mounted this file system with -o degraded? >>> >>> I'm going to guess the history is something like: >>> 1. enospc >>> 2. btrfs dev add >>> 3. some kind of filtered balance, which only causes data block groups >>> to be moved to the 2nd device >>> 4. 2nd device is physically removed without first 'btrfs dev del' >>> >>> Zirco's superblock very clearly says num_devices 2, so I'd expect >>> normal mount to always fail unless both devices are present. Is there >>> some weird edge case where Btrfs might permit non-degraded mount when >>> only data bg's are on a 2nd device? And then trouble only happens >>> later when a balance is done and it goes looking for these bg's? And >>> then, boom! >>> >>> -- >>> Chris Murphy -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
