Systems and methods are described for fully replacing an online first RAID group of data storage devices with a second RAID group of data storage devices, whereby the data is read in parallel from multiple devices in the first group and written in parallel to multiple devices in the second group. Sub-chunks of data chunks not currently storing any data may be bypassed from copying, as well as sub-chunks still storing data that is no longer in-use by a client. The data may be copied as-is rather than from and to the same logical block address on each respective group. A similar process may be applied for shrinking the number of storage devices allocating to a storage pool.