--- /dev/null
+
+ $ rbd create --size 20M img
+
+ $ DEV=$(sudo rbd map img)
+ $ blockdev --getiomin $DEV
+ 65536
+ $ blockdev --getioopt $DEV
+ 65536
+ $ cat /sys/block/${DEV#/dev/}/queue/discard_granularity
+ 65536
+ $ sudo rbd unmap $DEV
+
+ $ DEV=$(sudo rbd map -o alloc_size=512 img)
+ $ blockdev --getiomin $DEV
+ 512
+ $ blockdev --getioopt $DEV
+ 512
+ $ cat /sys/block/${DEV#/dev/}/queue/discard_granularity
+ 512
+ $ sudo rbd unmap $DEV
+
+ $ DEV=$(sudo rbd map -o alloc_size=4194304 img)
+ $ blockdev --getiomin $DEV
+ 4194304
+ $ blockdev --getioopt $DEV
+ 4194304
+ $ cat /sys/block/${DEV#/dev/}/queue/discard_granularity
+ 4194304
+ $ sudo rbd unmap $DEV
+
+ $ DEV=$(sudo rbd map -o alloc_size=8388608 img)
+ $ blockdev --getiomin $DEV
+ 4194304
+ $ blockdev --getioopt $DEV
+ 4194304
+ $ cat /sys/block/${DEV#/dev/}/queue/discard_granularity
+ 4194304
+ $ sudo rbd unmap $DEV
+
+ $ rbd rm --no-progress img