Calculate the average KB per read or write for an Oracle ASM disk: http://bommaritollc.com/2013/06/12/plotting-average-read-and-write-operation-size-by-asm-disk

asm_average_operation_size.sql

SELECT path, label, inst_id,
  (bytes_read / DECODE(reads, 0, 1, reads)) / 1024. AS kb_per_read, 
  (bytes_written / DECODE(writes, 0, 1, writes)) / 1024. AS kb_per_write
  FROM gv$asm_disk_stat
  ORDER BY path, inst_id;