Am 15.01.23 um 13:00 schrieb Pascal Hambourg:

Linux RAID supports TRIM/discard, but what does it do exactly ?
Does it only pass-through TRIM/discard information to the underlying 
devices or can it also store information about which blocks contain 
valid data in the superblock metadata?

pass-through TRIM/discard

it makes no sense to store that on the RAID layer - if someone is th 
eposition to store the information to reduce the fstrim load after a 
reboot it's the filesystem on-top

"filesystem -> luks -> lvm -> mdadm -> device" is a possible discard 
chain so why should mdadm store that information

if the filesystem knows "i notified that the blocks for deleteded file X 
are no longer in use" it can store that somewhere and none of the other 
layers would need to know because there won't be any discard request in 
the future