[feature] add support for enabling discard on a bcache device

[Dmitrii Shcherbakov]

Curtin and MAAS currently do not allow discard option to be configured on a bcache device (only cache set and cache mode are possible to set).

Discard is disabled by default.

https://wiki.ubuntu.com/ServerTeam/Bcache
make-bcache -C /dev/sdc -B /dev/sdb --discard --writeback
# ... --discard is for using TRIM on ssd, not activated by default.
https://www.kernel.org/doc/html/latest/admin-guide/bcache.html#sysfs-cache-device
"discard Boolean; if on a discard/TRIM will be issued to each bucket before it is reused. Defaults to off, since SATA TRIM is an unqueued command (and thus slow)."

https://github.com/CanonicalLtd/curtin/blob/ubuntu/18.1-50-g2d9b2c6f-0ubuntu1/curtin/commands/block_meta.py#L1188-L1208

[Adam Collard (adam-collard)]

This bug has not seen any activity in the last 6 months, so it is being automatically closed.

If you are still experiencing this issue, please feel free to re-open.

MAAS Team

[Blake Rouse (blake-rouse)]

I think this is something that curtin should be able to determine on the fly, if could check that that device is an SSD (or supports TRIM) and enable discard.

[Ryan Harper (raharper)]

there's no reason for curtin to determine on the fly; MAAS inventories the node, it knows which disks are rotational or ssd/nvme.

Curtin can extend the bcache syntax to allow discard to be enabled/disabled; However MAAS is the correct place to set the correct configuration.