Hi everybody,
when registering and mounting my bcache devices (unortunately my root
filesystem), the kernel informed me about `Detected obsoleted large
bucket layout, all attached bcache device will be read-only'.
Subsequently, my root fs was, in fact, read-only. Thus, I have no logs
for you unfortunately. As far as I remember, bcache-super-show showed
the same bucket and block sizes as always (except that the backing
device showed a clean cache state):
> bcache-super-show /dev/sda6
sb.magic ok
sb.first_sector 8 [match]
sb.csum C5EB3BA8CA523D61 [match]
sb.version 4 [backing device]
dev.label (empty)
dev.uuid 264d1acc-8461-4ddc-a825-f0acdeea3ede
dev.sectors_per_block 1
dev.sectors_per_bucket 1024
dev.data.first_sector 2048
dev.data.cache_mode 1 [writeback]
dev.data.cache_state 2 [dirty]
cset.uuid 755901be-a101-4581-b1d0-4d21d1619f27
> bcache-super-show /dev/sdb3
sb.magic ok
sb.first_sector 8 [match]
sb.csum BDA92F1E72DBA095 [match]
sb.version 3 [cache device]
dev.label (empty)
dev.uuid 25151c1a-904e-492e-b99b-6d07e13b047a
dev.sectors_per_block 1
dev.sectors_per_bucket 1024
dev.cache.first_sector 1024
dev.cache.cache_sectors 907564032
dev.cache.total_sectors 907565056
dev.cache.ordered yes
dev.cache.discard no
dev.cache.pos 0
dev.cache.replacement 0 [lru]
cset.uuid 755901be-a101-4581-b1d0-4d21d1619f27
For debugging purposes I tried to mount and chroot into my backing
device directly, using a loopback interface. I was not able to find an
offset for `losetup -f -o <offset> /dev/sda6', so that `mount -o loop
/dev/loop0 /mnt/mnt0' would not tell me that there was no filesystem.
Also, `for i in {0.2000}; do dd if=/dev/sda6 skip=$i | file -; done'
from [1] showed `data' for every offset.
After getting a little desperate, I booted into an older kernel
(although I didn't update my kernel or my bcache-tools since the last
boot) and everything worked. I then booted back into my current system
and everything worked again.
Is this a bug with bcache or do I need to change my setup to prevent
this from happening again? My bcache devices were created sometime
around 2015 or 2016.
System info:
uname -a: `Linux Horus 5.10.10-gentoo #1 SMP PREEMPT Mon Feb 15 15:00:49
CET 2021 x86_64 Intel(R) Core(TM) i7-4790K CPU @ 4.00GHz GenuineIntel
GNU/Linux'
bcache-tools version: 1.1
The older kernel is a 5.8.11-gentoo with voluntary preempt.
Best regards and thanks,
Constantin
[1]
https://stackoverflow.com/questions/22820492/how-to-revert-bcache-device-to-regular-device
