Rebuilding Depends on various variable for eg. disk size, disk speed, utility priority, and other processes running on the storage system. If there is high I/Os in the Storage System rebuilding will be slow, if its not stuck. However, you may also increase the rebuild priority.
Info： R5（7x 600Gb15K ） rebuilding very slow（200MB/h），array cx340（flare 3.26）  My question is： 1、Why rebuilding process so slowlly 2、How to speed up the rebuilding process
R5 rebuilding very slow