feature request: Have an equivalent to «device evacuate» for a combination of «[devices (sda sdb...)] + data type»

ticpu commented 3 years ago

As a system administrator, after changing the data replication settings, I want to be able to enforce the new settings with a command that allows to select items from the replicas section of «bcachefs fs usage».

Right now, a workaround is to evacuate one of the device appearing as grouped together.

With this new command, it'd be possible to ensure, for example;

sda doesn't contain any btree data (enforcing that the HDD doesn't contain any btree data).
[sda sdb] do not contain user data (enforcing a downgrade from data_replicas=2 to data_replicas=1).
sdc does not contain cached data (enforcing an HDD doesn't contain any cached data).
(any device) does not contain parity data (enforcing disabling erasure_coding).

ticpu commented 2 years ago

@YellowOnion I'm curious to know what triggered closing this issue. I haven't been following the project as much lately.

YellowOnion commented 2 years ago

I was just closing all older bugs, I now see that this is a feature request, my bad, Though I can't really tell what the use case is for this.

bcachefs is "garbage collected", when you lower the replication count it just treats all extra copies as reclaimable space, (part of the nature of CoW) that can be later reused, these stats can be deceptive because of that.

@koverstreet can you chime in?

koverstreet / bcachefs

feature request: Have an equivalent to «device evacuate» for a combination of «[devices (sda sdb...)] + data type» #182