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 discards actually work even without raid456.devices_handle_discard_safely=Y, but aren't passed via the DM device. > 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: >> >> 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. >> >> If you create a dm-era device over a normal block device without mdadm RAID5 or even over mdadm >> RAID1 - it will preserve discard support. >> >> Why? How can it be fixed? >> >> -- >> With best regards, >> Vitaliy Filippov >> >> -- >> dm-devel mailing list >> dm-devel@xxxxxxxxxx >> https://listman.redhat.com/mailman/listinfo/dm-devel > > -- > dm-devel mailing list > dm-devel@xxxxxxxxxx > https://listman.redhat.com/mailman/listinfo/dm-devel -- dm-devel mailing list dm-devel@xxxxxxxxxx https://listman.redhat.com/mailman/listinfo/dm-devel
