Dear Robert,
thank you for all the possibilities! I think option 4 + 3 would be my
prefered ones.
Until I received your answer I allready played around with that volume
and converting it to Raid 5 seems to work too, I'll attach the steps I
took. Soon I'll try your solution and do some checksuming to verify the
integrity of the files that were written while I pulled out the drive.
Please check in the steps below that I can violate Raid6 geometry by
removing sdk again.
--------------------
$ btrfs fi sh
Label: none uuid: 28410e37-77c1-4c01-8075-0d5068d9ffc2
Total devices 4 FS bytes used 257.05GiB
devid 1 size 465.76GiB used 262.03GiB path /dev/sdi1
devid 2 size 465.76GiB used 262.00GiB path /dev/sdj1
devid 3 size 465.76GiB used 261.03GiB path /dev/sdh1
devid 4 size 465.76GiB used 0.00 path /dev/sdk1
$ btrfs fi balance start -dconvert=raid5 /mnt
Done, had to relocate 261 out of 263 chunks
$ btrfs fi sh
Label: none uuid: 28410e37-77c1-4c01-8075-0d5068d9ffc2
Total devices 4 FS bytes used 257.09GiB
devid 1 size 465.76GiB used 262.03GiB path /dev/sdi1
devid 2 size 465.76GiB used 262.00GiB path /dev/sdj1
devid 3 size 465.76GiB used 261.03GiB path /dev/sdh1
devid 4 size 465.76GiB used 0.00 path /dev/sdk1
$ btrfs fi df /mnt
Data, RAID5: total=522.00GiB, used=256.82GiB
System, RAID1: total=32.00MiB, used=56.00KiB
Metadata, RAID1: total=1.00GiB, used=271.49MiB
$ btrfs de de /dev/sdk1 /mnt
$ btrfs fi sh
Label: none uuid: 28410e37-77c1-4c01-8075-0d5068d9ffc2
Total devices 3 FS bytes used 257.09GiB
devid 1 size 465.76GiB used 262.03GiB path /dev/sdi1
devid 2 size 465.76GiB used 262.00GiB path /dev/sdj1
devid 3 size 465.76GiB used 261.03GiB path /dev/sdh1
$ btrfs de ad /dev/sdk1 /mnt
/dev/sdk1 appears to contain an existing filesystem (btrfs).
Use the -f option to force overwrite.
$ btrfs de ad -f /dev/sdk1 /mnt
/dev/sdk1 is mounted
$ mount
...
/dev/sdi1 on /mnt type btrfs (rw,degraded)
$ mount -t btrfs -o remount,rw /dev/sdi1 /mnt
$ btrfs de ad -f /dev/sdk1 /mnt
/dev/sdk1 is mounted
$ umount /dev/sdk1
umount: /dev/sdk1 ist nicht eingehängt
$ dd if=/dev/zero of=/dev/sdk bs=1M count=100
100+0 Datensätze ein
100+0 Datensätze aus
104857600 Bytes (105 MB) kopiert, 1,68492 s, 62,2 MB/s
$ fdisk /dev/sdk # o+n+w
$ btrfs de ad -f /dev/sdk1 /mnt
/dev/sdk1 is mounted
# still not able to mount sdk, but this is most likely the cause:
$ btrfs fi sh /dev/sdk1
Label: none uuid: 28410e37-77c1-4c01-8075-0d5068d9ffc2
Total devices 3 FS bytes used 257.09GiB
devid 1 size 465.76GiB used 262.03GiB path /dev/sdi1
devid 2 size 465.76GiB used 262.00GiB path /dev/sdj1
devid 3 size 465.76GiB used 261.03GiB path /dev/sdh1
$ wipefs /dev/sdk1
# this did not help, wipefs does not see any signatures
# I don't know what I did yesterday, but it suddently worked:
$ btrfs de ad -f /dev/sdk1 /mnt
$ btrfs fi sh
Label: none uuid: 28410e37-77c1-4c01-8075-0d5068d9ffc2
Total devices 4 FS bytes used 257.05GiB
devid 1 size 465.76GiB used 131.00GiB path /dev/sdi1
devid 2 size 465.76GiB used 130.03GiB path /dev/sdj1
devid 3 size 465.76GiB used 131.03GiB path /dev/sdh1
devid 4 size 465.76GiB used 0.00 path /dev/sdk1
$ btrfs fi balance start -dconvert=raid6 /mnt
Done, had to relocate 130 out of 132 chunks
$ btrfs fi sh
Label: none uuid: 28410e37-77c1-4c01-8075-0d5068d9ffc2
Total devices 4 FS bytes used 257.09GiB
devid 1 size 465.76GiB used 131.00GiB path /dev/sdi1
devid 2 size 465.76GiB used 130.03GiB path /dev/sdj1
devid 3 size 465.76GiB used 131.03GiB path /dev/sdh1
devid 4 size 465.76GiB used 130.00GiB path /dev/sdk1
$ btrfs de de /dev/sdk1 /mnt
# now I can remove sdk and violate Raid6 geometry:
$ btrfs fi sh
Label: none uuid: 28410e37-77c1-4c01-8075-0d5068d9ffc2
Total devices 3 FS bytes used 257.03GiB
devid 1 size 465.76GiB used 267.00GiB path /dev/sdi1
devid 2 size 465.76GiB used 266.03GiB path /dev/sdj1
devid 3 size 465.76GiB used 267.03GiB path /dev/sdh1
$ btrfs fi df /mnt
Data, RAID6: total=266.00GiB, used=256.77GiB
System, RAID1: total=32.00MiB, used=52.00KiB
Metadata, RAID1: total=1.00GiB, used=270.72MiB
$ btrfs fi sh
Label: none uuid: 28410e37-77c1-4c01-8075-0d5068d9ffc2
Total devices 4 FS bytes used 257.05GiB
devid 1 size 465.76GiB used 262.03GiB path /dev/sdi1
devid 2 size 465.76GiB used 262.00GiB path /dev/sdj1
devid 3 size 465.76GiB used 261.03GiB path /dev/sdh1
devid 4 size 465.76GiB used 0.00 path /dev/sdk1
$ btrfs fi balance start -dconvert=raid5 /mnt
Done, had to relocate 261 out of 263 chunks
$ btrfs fi sh
Label: none uuid: 28410e37-77c1-4c01-8075-0d5068d9ffc2
Total devices 4 FS bytes used 257.09GiB
devid 1 size 465.76GiB used 262.03GiB path /dev/sdi1
devid 2 size 465.76GiB used 262.00GiB path /dev/sdj1
devid 3 size 465.76GiB used 261.03GiB path /dev/sdh1
devid 4 size 465.76GiB used 0.00 path /dev/sdk1
$ btrfs fi df /mnt
Data, RAID5: total=522.00GiB, used=256.82GiB
System, RAID1: total=32.00MiB, used=56.00KiB
Metadata, RAID1: total=1.00GiB, used=271.49MiB
$ btrfs de de /dev/sdk1 /mnt
$ btrfs fi sh
Label: none uuid: 28410e37-77c1-4c01-8075-0d5068d9ffc2
Total devices 3 FS bytes used 257.09GiB
devid 1 size 465.76GiB used 262.03GiB path /dev/sdi1
devid 2 size 465.76GiB used 262.00GiB path /dev/sdj1
devid 3 size 465.76GiB used 261.03GiB path /dev/sdh1
$ btrfs de ad /dev/sdk1 /mnt
/dev/sdk1 appears to contain an existing filesystem (btrfs).
Use the -f option to force overwrite.
$ btrfs de ad -f /dev/sdk1 /mnt
/dev/sdk1 is mounted
$ mount
...
/dev/sdi1 on /mnt type btrfs (rw,degraded)
$ mount -t btrfs -o remount,rw /dev/sdi1 /mnt
$ btrfs de ad -f /dev/sdk1 /mnt
/dev/sdk1 is mounted
$ umount /dev/sdk1
umount: /dev/sdk1 ist nicht eingehängt
$ dd if=/dev/zero of=/dev/sdk bs=1M count=100
100+0 Datensätze ein
100+0 Datensätze aus
104857600 Bytes (105 MB) kopiert, 1,68492 s, 62,2 MB/s
$ fdisk /dev/sdk # o+n+w
$ btrfs de ad -f /dev/sdk1 /mnt
/dev/sdk1 is mounted
# still not able to mount sdk, but this is most likely the cause:
$ btrfs fi sh /dev/sdk1
Label: none uuid: 28410e37-77c1-4c01-8075-0d5068d9ffc2
Total devices 3 FS bytes used 257.09GiB
devid 1 size 465.76GiB used 262.03GiB path /dev/sdi1
devid 2 size 465.76GiB used 262.00GiB path /dev/sdj1
devid 3 size 465.76GiB used 261.03GiB path /dev/sdh1
$ wipefs /dev/sdk1
# this did not help, wipefs does not see any signatures
# I don't know what I did yesterday, but it suddently worked:
$ btrfs de ad -f /dev/sdk1 /mnt
$ btrfs fi sh
Label: none uuid: 28410e37-77c1-4c01-8075-0d5068d9ffc2
Total devices 4 FS bytes used 257.05GiB
devid 1 size 465.76GiB used 131.00GiB path /dev/sdi1
devid 2 size 465.76GiB used 130.03GiB path /dev/sdj1
devid 3 size 465.76GiB used 131.03GiB path /dev/sdh1
devid 4 size 465.76GiB used 0.00 path /dev/sdk1
$ btrfs fi balance start -dconvert=raid6 /mnt
Done, had to relocate 130 out of 132 chunks
$ btrfs fi sh
Label: none uuid: 28410e37-77c1-4c01-8075-0d5068d9ffc2
Total devices 4 FS bytes used 257.09GiB
devid 1 size 465.76GiB used 131.00GiB path /dev/sdi1
devid 2 size 465.76GiB used 130.03GiB path /dev/sdj1
devid 3 size 465.76GiB used 131.03GiB path /dev/sdh1
devid 4 size 465.76GiB used 130.00GiB path /dev/sdk1
$ btrfs de de /dev/sdk1 /mnt
# now I can remove sdk and violate Raid6 geometry:
$ btrfs fi sh
Label: none uuid: 28410e37-77c1-4c01-8075-0d5068d9ffc2
Total devices 3 FS bytes used 257.03GiB
devid 1 size 465.76GiB used 267.00GiB path /dev/sdi1
devid 2 size 465.76GiB used 266.03GiB path /dev/sdj1
devid 3 size 465.76GiB used 267.03GiB path /dev/sdh1
$ btrfs fi df /mnt
Data, RAID6: total=266.00GiB, used=256.77GiB
System, RAID1: total=32.00MiB, used=52.00KiB
Metadata, RAID1: total=1.00GiB, used=270.72MiB
Am 01.12.2014 um 20:33 schrieb Robert White:
On 12/01/2014 06:47 AM, Oliver wrote:
Hi All,
on a testing machine I installed four HDDs and they are configured as
RAID6. For a test I removed one of the drives (/dev/sdk) while the
volume was mounted and data was written to it. This worked well, as far
as I can see. Some I/O errors were written to /var/log/syslog, but the
volume kept working. Unfortunately the command "btrfs fi sh" did not
show any missing drives. So I remounted the volume in degraded mode:
"mount -t btrfs /dev/sdx1 -o remount,rw,degraded,noatime /mnt". This way
the drive in question was reported as missing. Then I plugged in the HDD
again (it is of course /dev/sdk again) and started a balancing in hope
that this will restore RAID6: "btrfs filesystem balance start /mnt". Now
the volume looks like this:
Since it was already running and such, remounting it as degraded was
probably not a good thing (or even vaguely necessary).
The WIKI, in discussing add/remove and failed drives goes to great
lengths (big red box) to discuss the current instability of RAID5/6 format.
I am guessing here but I _think_ you should do the following...
(0) Backup your data. [okay this is a test system that you deliberately
purturbed but still... 8-) ]
Option 1:
(reasonable, but undocumented .. Either blance or scrub _ought_ to look
at the disk sectors and trigger some re-copying from the good parts.)
The disk is in the array (again), you may just need to re-balance or
scrub the array to get the data on the drive back in harmony with the
state of the array overall.
Option 2:
(unlikely :: add and remove are about making the geometry smaller/larger
and, as stated, a RAID 6 cannot be less than 4 drives by definition, so
there is no three-drive geometry for a RAID 6.)
re-unplug the device, then use btrfs remove /dev/sdk /mnt
then re-plug-in the device and use btrfs add /dev/sdk /mnt
Option 3:
(reasonable, but undocumented :: replace by device id -- 4 in your
example case -- instead of system path. This would, I should think, skip
the check of /dev/sdk1's separate status)
btrfs replace start -f 4 /dev/sdk1 /mnt
Option 3a:
(got to get /dev/sdk1 back out of the list of active devices for /mnt so
the system wont see /dev/sdk1 as "mounted" (e.g. held by a subsystem))
unplug device.
mount -o remount,degraded etc...
plug in device.
btrfs replace start -f 4 /dev/sdk1 /mnt
Option 4:
(most likely, most time consuming)
Unplug /dev/sdk. Plug it into another computer and zero a decent chunk
of partition 1.
Plug it back into the original computer
do the replace operation as in Option 3.
This is the most-likely correct option if a simple rebalance or scrub
doesn't work, as you will be presenting the system with three attached
drives, one "missing" drive that will not match any necessary
signatures, and a "new, blank" drive in its place.
===
In all cases, you may need to unmount or remount or remount degraded in
there somewhere, particularly because you have already done so at least
once.
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