Defragmentation is connected with a lot of disk io activity and it requires 2 * blob_size as a free space on the device. Currently, defragmentation kills disk of backend and all read/write operations with backends are dramatically slowed down. Also free space requirement reserves space on each backend device, as a result we have 2 * blob_size * number of backends reserved but mostly unused space.
Solution
Make defragmentation on dedicated device. Lets make comparison of defragmentation on dedicated device vs backend's device:
Measurement
dedicated device
backend's device
disk io
1 read and 1 write at the backend's device and 3 read and 3 write at the dedicated device
3 read, 3 write and 1 move at the backend's device
free space requirement for one server
2 * blob_size on dedicated device
2 * blob_size * number of backends
Since defragmentation will have most of disk io at dedicated disk, backend's disk will be free for clients requests.
Problem
Defragmentation is connected with a lot of disk io activity and it requires
2 * blob_sizeas a free space on the device. Currently, defragmentation kills disk of backend and all read/write operations with backends are dramatically slowed down. Also free space requirement reserves space on each backend device, as a result we have2 * blob_size * number of backendsreserved but mostly unused space.Solution
Make defragmentation on dedicated device. Lets make comparison of defragmentation on dedicated device vs backend's device:
2 * blob_sizeon dedicated device2 * blob_size * number of backendsSince defragmentation will have most of disk io at dedicated disk, backend's disk will be free for clients requests.