If there is a read request during rebuild, data is read by sequentially switching a plurality of disk devices in a certain block size unit lower than a block size in which {HEAD ~ each disk device} reads {TAIL ~ data} during normal read 
reads
If there is a read request during rebuild , data is read by sequentially switching a plurality of disk devices in a certain block size unit lower than a block size in which { HEAD ~ each disk device } reads { TAIL ~ data } during normal read
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH