Re: ont out of 6 bcache devices does not register automatically

Stefan Priebe - Profihost AG
2017-11-23T07:10:08Z

Hello,

i got it...

first of all the same issue still applies to util-linux v2.31 which is
the latest upstream version.

# ./blkid --version
lt-blkid from util-linux 2.31 (libblkid 2.31.0, 19-Oct-2017)

# ./blkid -o udev -p /dev/sdf1
ID_FS_AMBIVALENT=other:bcache other:xfs_external_log

The issue is somewhat different. The device is used for ceph which
stores on on that Disk 4MB slices of VM block devices.

So we have:
bcache => XFS on top => thousands of files containing VM images => XFS
in those images

So the xfs_external_log superblock which is seen by blkid is in reality
a superblock of a VM image inside a file which is saved in bcache.

This make even more sense as the system was bootable without any
problems for the last few years without swapping a disk. But somewhat
now a VM image file has exactly positioned it's superblock on a position
blkid expects a superblock.

I see no way to solve it except for changing the udev rules file which
comes with bcache-tools.

Instead of only checking:
ENV{ID_FS_TYPE}=="bcache", GOTO="bcache_backing_found"

it also needs to check for:
ID_FS_AMBIVALENT=other:bcache

Any opinions or suggestions?

Greets,
Stefan

Am 22.11.2017 um 22:13 schrieb Stefan Priebe - Profihost AG:
>
> Am 22.11.2017 um 22:10 schrieb Michael Lyle:
>> On 11/22/2017 01:07 PM, Stefan Priebe - Profihost AG wrote:
>>> default debian jessie version:
>>> # blkid -v
>>> blkid from util-linux 2.25.2 (libblkid 2.25.0, 24-Oct-2014)
>>
>> OK, so it's ancient.
>>
>> One other thing that can get you-- if there was ever an xfs or other
>> filesystem on this disk -without- bcache, then you created bcache & xfs
>> on it without wipefs... the old superblock can still be hanging around
>> and not having happened to been rewritten.
>
> no there shouldn't eb ever an xfs without it on disk - but i can't
> guarantee that.
>
> To reproduce the isue you need the first 10MB of the disk.
>
> See below:
>
> Still ok:
>
> # dd if=/dev/sdf1 of=/tmp/8k bs=8M count=1
> 1+0 records in
> 1+0 records out
> 8388608 bytes (8,4 MB) copied, 0,01318 s, 636 MB/s
> # /sbin/blkid -o udev -p /tmp/8k
> ID_FS_UUID=65811163-4ffc-4823-ad72-bae10ce85b63
> ID_FS_UUID_ENC=65811163-4ffc-4823-ad72-bae10ce85b63
> ID_FS_TYPE=bcache
> ID_FS_USAGE=other
>
> not anymore:
>
> # dd if=/dev/sdf1 of=/tmp/8k bs=10M count=1
> 1+0 records in
> 1+0 records out
> 10485760 bytes (10 MB) copied, 0,0115798 s, 906 MB/s
> # /sbin/blkid -o udev -p /tmp/8k
> ID_FS_AMBIVALENT=other:bcache other:xfs_external_log
>
> Stefan
>
>>
>> Mike
>>
>>>
>>>>
>>>> Mike
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>>