On Fri, Jan 03, 2014 at 05:56:42PM -0500, Jim Salter wrote: > I actually read the wiki pretty obsessively before blasting the list > - could not successfully find anything answering the question, by > scanning the FAQ or by Googling. > > You're right - mount -t btrfs -o degraded /dev/vdb /test worked fine. > > HOWEVER - this won't allow a root filesystem to mount. How do you > deal with this if you'd set up a btrfs-raid1 or btrfs-raid10 as your > root filesystem? Few things are scarier than seeing the "cannot find > init" message in GRUB and being faced with a BusyBox prompt...
Use grub's command-line editing to add rootflags=degraded to it. Hugo. > which > is actually how I initially got my scare; I was trying to do a > walkthrough for setting up a raid1 / for an article in a major > online magazine and it wouldn't boot at all after removing a device; > I backed off and tested with a non root filesystem before hitting > the list. > > I did find the -o degraded argument in the wiki now that you > mentioned it - but it's not prominent enough if you ask me. =) > > > > On 01/03/2014 05:43 PM, Joshua Schüler wrote: > >Am 03.01.2014 23:28, schrieb Jim Salter: > >>I'm using Ubuntu 12.04.3 with an up-to-date 3.11 kernel, and the > >>btrfs-progs from Debian Sid (since the ones from Ubuntu are ancient). > >> > >>I discovered to my horror during testing today that neither raid1 nor > >>raid10 arrays are fault tolerant of losing an actual disk. > >> > >>mkfs.btrfs -d raid10 -m raid10 /dev/vdc /dev/vdd /dev/vdd /dev/vde > >>mkdir /test > >>mount /dev/vdb /test > >>echo "test" > /test/test > >>btrfs filesystem sync /test > >>shutdown -hP now > >> > >>After shutting down the VM, I can remove ANY of the drives from the > >>btrfs raid10 array, and be unable to mount the array. In this case, I > >>removed the drive that was at /dev/vde, then restarted the VM. > >> > >>btrfs fi show > >>Label: none uuid: 94af1f5d-6ad2-4582-ab4a-5410c410c455 > >> Total devices 4 FS bytes used 156.00KB > >> devid 3 size 1.00GB used 212.75MB path /dev/vdd > >> devid 3 size 1.00GB used 212.75MB path /dev/vdc > >> devid 3 size 1.00GB used 232.75MB path /dev/vdb > >> *** Some devices missing > >> > >>OK, we have three of four raid10 devices present. Should be fine. Let's > >>mount it: > >> > >>mount -t btrfs /dev/vdb /test > >>mount: wrong fs type, bad option, bad superblock on /dev/vdb, > >> missing codepage or helper program, or other error > >> In some cases useful info is found in syslog - try > >> dmesg | tail or so > >> > >>What's the kernel log got to say about it? > >> > >>dmesg | tail -n 4 > >>[ 536.694363] device fsid 94af1f5d-6ad2-4582-ab4a-5410c410c455 devid 1 > >>transid 7 /dev/vdb > >>[ 536.700515] btrfs: disk space caching is enabled > >>[ 536.703491] btrfs: failed to read the system array on vdd > >>[ 536.708337] btrfs: open_ctree failed > >> > >>Same behavior persists whether I create a raid1 or raid10 array, and > >>whether I create it as that raid level using mkfs.btrfs or convert it > >>afterwards using btrfs balance start -dconvert=raidn -mconvert=raidn. > >>Also persists even if I both scrub AND sync the array before shutting > >>the machine down and removing one of the disks. > >> > >>What's up with this? This is a MASSIVE bug, and I haven't seen anybody > >>else talking about it... has nobody tried actually failing out a disk > >>yet, or what? > >Hey Jim, > > > >keep calm and read the wiki ;) > >https://btrfs.wiki.kernel.org/ > > > >You need to mount with -o degraded to tell btrfs a disk is missing. > > > > > >Joshua > > > > > -- === Hugo Mills: hugo@... carfax.org.uk | darksatanic.net | lug.org.uk === PGP key: 65E74AC0 from wwwkeys.eu.pgp.net or http://www.carfax.org.uk --- Eighth Army Push Bottles Up Germans -- WWII newspaper --- headline (possibly apocryphal)
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