Hi
Just to note, the problem is solved by setting
raid456.devices_handle_discard_safely=Y in kernel command line.
It seems that dm-table.c checks for blk_queue_discard() of underlying devices
and RAID5 device has the QUEUE_FLAG_DISCARD unset and at the same time
discard_granularity != 0. So di
Even worse, dm-linear has the same problem.
dm-linear over mdadm RAID5 doesn't support discard while mdadm device itself
supports it.
> Hi!
>
> A dm-era device created over a RAID5 array loses discard support.
>
> Test script is attached.
>
> If you run it on SSD you'll see something like:
>
Hi!
A dm-era device created over a RAID5 array loses discard support.
Test script is attached.
If you run it on SSD you'll see something like:
loop0 4096
loop1 4096
loop2 4096
loop3 4096
md55 1048576
loop_test_era 0
I.e. mdadm device supports discard, but dm-era device started over it doesn't.
