In the RESTBase Cassandra cluster, data distributed over the JBOD devices, isn't always very balanced (some are more imbalanced than others). For example:
restbase1007
~# df -h Filesystem Size Used Avail Use% Mounted on udev 10M 0 10M 0% /dev tmpfs 26G 2.5G 23G 10% /run /dev/md0 28G 4.5G 22G 18% / tmpfs 63G 0 63G 0% /dev/shm tmpfs 5.0M 0 5.0M 0% /run/lock tmpfs 63G 0 63G 0% /sys/fs/cgroup /dev/sdd4 893G 544G 349G 61% /srv/sdd4 /dev/sdb4 893G 528G 365G 60% /srv/sdb4 /dev/sdc4 893G 587G 306G 66% /srv/sdc4 /dev/sda4 893G 368G 525G 42% /srv/sda4 /dev/sde4 893G 278G 615G 32% /srv/sde4 /dev/md2 46G 23G 21G 52% /srv/cassandra/instance-data ~# du -shc /srv/sd[a-e]4/cassandra-{a,b,c} 105G /srv/sda4/cassandra-a 172G /srv/sdb4/cassandra-a 205G /srv/sdc4/cassandra-a 113G /srv/sdd4/cassandra-a 53G /srv/sde4/cassandra-a 76G /srv/sda4/cassandra-b 147G /srv/sdb4/cassandra-b 171G /srv/sdc4/cassandra-b 189G /srv/sdd4/cassandra-b 106G /srv/sde4/cassandra-b 188G /srv/sda4/cassandra-c 210G /srv/sdb4/cassandra-c 212G /srv/sdc4/cassandra-c 243G /srv/sdd4/cassandra-c 120G /srv/sde4/cassandra-c 2.3T total ~#