Bcacheを利用すると、Read IOPSが大幅に上昇させる事ができる。

JuJu + MAAS + OpenStackで構成している事を想定で説明

OSD_UNIT=ceph-osd/0
OSD=osd.1
OSD_ID=1
OSD_DNAME=/dev/bcache0
OSD_PV=/dev/nvme1n1
OSD_VG=ceph-9bc57db6-c7d6-4ff9-91e2-1829e3e766aa

ceph osd out $OSD

juju run-action --wait ceph-mon/leader change-osd-weight osd=$OSD_ID weight=0
juju run-action --wait $OSD_UNIT stop osds=$OSD_ID

juju ssh $OSD_UNIT
sudo vgremove -y $OSD_VG
sudo pvremove -y $OSD_PV

juju run-action --wait ceph-mon/leader purge-osd osd=$OSD_ID i-really-mean-it=yes

make-bcache -B /dev/nvme1n1 -C /dev/nvme0n1
echo writeback > /sys/block/bcache0/bcache/cache_mode

juju run-action --wait $OSD_UNIT zap-disk devices=$OSD_DNAME i-really-mean-it=yes
juju run-action --wait $OSD_UNIT add-disk osd-devices=$OSD_DNAME