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I've been exploring Btrfs in hopes of using it to store large files I use infrequently. I've configured a subvolume and began copying data to it. During the copy operation, the filesystem entered read-only mode, and it became impossible to re-mount the volumes after unmounting them ("Remounting read-write after error is not allowed").
/etc/fstab:
UUID=c555d6b2-04e9-4659-861e-2beee5bdfe01 /mnt/btrfs btrfs defaults,noauto,user,relatime,rw 0 0
UUID=c555d6b2-04e9-4659-861e-2beee5bdfe01 /srv/disks btrfs defaults,noauto,user,relatime,rw,nodev,subvol=.subvolume/disks,compress 0 0The attempted operation:
[root@glen-arch whatcd]# cp -a /mnt/media/Disks/* /srv/disks
# After a delay in which a few files were successfully copied...
cp: cannot create regular file ‘/srv/disks/rpi.iso’: Read-only file system
cp: cannot create regular file ‘/srv/disks/rtc.iso’: Read-only file system
[root@glen-arch whatcd]# umount /srv/disks
[root@glen-arch whatcd]# umount /mnt/btrfs
[root@glen-arch whatcd]# mount /mnt/btrfs
mount: wrong fs type, bad option, bad superblock on /dev/sdb1,
missing codepage or helper program, or other error
In some cases useful info is found in syslog - try
dmesg | tail or so.The output from dmesg contains a plethora of these:
[ 1760.622614] sd 1:0:0:0: [sdb] CDB:
[ 1760.622614] cdb[0]=0x2a: 2a 00 00 4b 63 60 00 04 00 00
[ 1760.622650] sd 1:0:0:0: [sdb] Unhandled error code
[ 1760.622651] sd 1:0:0:0: [sdb]
[ 1760.622651] Result: hostbyte=0x04 driverbyte=0x00Attempting to remount caused dmesg to output a warning and a call trace:
[ 2057.825247] WARNING: CPU: 0 PID: 6991 at fs/sync.c:55 sync_filesystem+0xa1/0xb0()
[ 2057.825362] CPU: 0 PID: 6991 Comm: mount Tainted: G WC O 3.16.1-1-ARCH #1
[ 2057.825364] Hardware name: ASUSTeK COMPUTER INC. N76VJ/N76VJ, BIOS N76VJ.202 08/31/2012
[ 2057.825367] 0000000000000000 0000000003f22fcb ffff88015d863c50 ffffffff8152ae6c
[ 2057.825371] 0000000000000000 ffff88015d863c88 ffffffff8106e45d ffff88021acf8800
[ 2057.825374] ffff88015d863dbc 0000000070810001 0000000000001000 ffff88021ae04000
[ 2057.825378] Call Trace:
[ 2057.825385] [<ffffffff8152ae6c>] dump_stack+0x4d/0x6f
[ 2057.825392] [<ffffffff8106e45d>] warn_slowpath_common+0x7d/0xa0
[ 2057.825395] [<ffffffff8106e58a>] warn_slowpath_null+0x1a/0x20
[ 2057.825400] [<ffffffff811f26a1>] sync_filesystem+0xa1/0xb0
[ 2057.825413] [<ffffffffa0974c73>] btrfs_remount+0x93/0x510 [btrfs]
[ 2057.825419] [<ffffffff811569f0>] ? free_pages.part.64+0x40/0x50
[ 2057.825429] [<ffffffffa0975543>] btrfs_mount+0x453/0x950 [btrfs]
[ 2057.825434] [<ffffffff8119a191>] ? alloc_pages_current+0xb1/0x160
[ 2057.825439] [<ffffffff811c6058>] mount_fs+0x38/0x1c0
[ 2057.825443] [<ffffffff811e0e17>] vfs_kern_mount+0x67/0x120
[ 2057.825447] [<ffffffff811e3847>] do_mount+0x247/0xae0
[ 2057.825451] [<ffffffff811e4404>] SyS_mount+0x94/0xf0
[ 2057.825456] [<ffffffff81530be9>] system_call_fastpath+0x16/0x1b
[ 2057.825458] ---[ end trace 8b86846916e07f4a ]---
[ 2057.825462] BTRFS info (device sdb1): disk space caching is enabled
[ 2057.825465] BTRFS error (device sdb1): Remounting read-write after error is not allowedI realize Btrfs is still experimental, but this seems like a fairly basic configuration. Is there something obvious I'm missing, or is there perhaps an error with the disk itself?
Last edited by goakley (2014-09-02 14:56:24)
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This:
[ 1760.622614] sd 1:0:0:0: [sdb] CDB:
[ 1760.622614] cdb[0]=0x2a: 2a 00 00 4b 63 60 00 04 00 00
[ 1760.622650] sd 1:0:0:0: [sdb] Unhandled error code
[ 1760.622651] sd 1:0:0:0: [sdb]
[ 1760.622651] Result: hostbyte=0x04 driverbyte=0x00...hints at a potential problem with your hardware. Could you run the same tests using another filesystem to confirm?
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You seem to be correct; running tests with ext4 yields the same CDB problem! Thank you for your help.
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