I''ve recently setup a system (Kernel 3.12.5-1-ARCH) which is layered as
follows:
/dev/sdb3 - cache0 (80 GB Intel SSD)
/dev/sdc1 - backing device (2 TB WD HDD)
sdb3+sdc1 => /dev/bcache0
On /dev/bcache0, there''s a btrfs filesystem with 2 subvolumes, mounted
as / and /home. What''s been bothering me are the following entries in
my kernel log:
[13811.845540] incomplete page write in btrfs with offset 1536 and length 2560
[13870.326639] incomplete page write in btrfs with offset 3072 and length 1024
The offset/length values are always either 1536/2560 or 3072/1024,
they sum up nicely to 4K. There are 607 of those in there as I am
writing this, the machine has been up 18 hours and been under no
particular I/O strain (it''s a desktop).
Trying to fix this, I unattached the cache (still using /dev/bcache0,
but without /dev/sdb3 attached), causing these errors to disappear. As
soon as I re-attached /dev/sdb3 they started again, so I am fairly
sure it''s an unfavorable interaction between bcache and btrfs.
Is this something I should be worried about (they''re only emitted with
KERN_INFO?) or just an alignment problem? The underlying HDD is using
4K-Sectors, while the block_size of bcache seems to be 512, could that
be the issue here?
I''ve also encountered incomplete reads and a few csum errors, but I
have not been able to trigger these regularly. I have a feeling that
the error is more likely o be on the bcache end (I''ve mailed to that
list as well), however any insight into the matter would be much
appreciated.
Thanks,
- eb
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