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