Dear btrfs-team,
I am aware, that barriers are essential for btrfs [1].
I have some questions on that topic:
1) I am not aware how to determine, whether barriers are supported,
except for searching dmesg for a message that barriers are disabled. Is
that correct? It would be nice, if that could be determined before
creating the FS.
2) I find the location of the (only?) warning -dmesg- well hidden. I
think it would be better to notify the user when creating the
file-system.
3) Even more, it would be good, if btrfs would disable the write cache
in that case, so that one does not need to rely on the user
4) If [2] is still valid, there are drives 'lying' about their barrier
support. Can someone comment? If that is the case, it would be even
advisable to provide a test to test the actual capability. In fact, if
this is still valid, this may be the reason for some btrfs corruptions
that have been discussed here. [I did read, that LVM/Device-Mapper does
not support barriers, but I think that this is outdated]
Greetings,
Hendrik
[1]
https://btrfs.wiki.kernel.org/index.php/FAQ#I_see_a_warning_in_dmesg_about_barriers_being_disabled_when_mounting_my_filesystem._What_does_that_mean.3F
[2] https://brad.livejournal.com/2116715.html
