Any subsequent failure during the reconstruction within the same array (second drive failure,  second coincident medium errors, or a drive failure and a medium error) can be recovered  without data loss. Performance of the RAID 6 array returns to normal when the data reconstruction on the spare  drive is complete. The rebuild time varies, depending on the capacity of the failed drive and  the workload on the array and the DA. The completion time is comparable to a RAID 5 rebuild,  but slower than rebuilding a RAID 10 array in a single drive failure.  RAID 10 provides high availability by combining features of RAID 0 and RAID 1. RAID 0  optimizes performance by striping volume data across multiple drives. RAID 1 provides drive  mirroring, which duplicates data between two drives. By combining the features of RAID 0  and RAID 1, RAID 10 provides a second optimization for fault tolerance. Data is striped  across half of the drives in the RAID 1 array. The same data is also striped across the other  half of the array, which creates a mirror. Access to data is preserved if one drive in each  mirrored pair remains available. RAID 10 offers faster data reads and writes than RAID 6 or  RAID 5 because it does not need to manage parity. However, with half of the drives in the  group used for data and the other half mirroring that data, RAID 10 arrays have less usable  capacity than RAID 6 or RAID 5 arrays. Note:  RAID 10 is not supported for the 7.68 TB and 15.36 TB High-Capacity Flash drives RAID 10 is commonly used for workloads that require the highest performance from the drive  subsystem. Although with RAID 6, each front-end random write I/O might theoretically lead to  6 back-end I/Os including the parity updates (RAID penalty), this number is 4 for a RAID 5  and only 2 for a RAID 10 (not counting cache optimizations). Typical areas of operation for  RAID 10 are workloads with a high random-write ratio. Either member in the mirrored pair can  respond to the read requests. In the DS8880, the RAID 10 implementation is achieved by using six or eight drives. If spares  need to be allocated from the array site, six drives are used to make a three-drive RAID 0  array, which is then mirrored to a three-drive array (3x3). If spares do not need to be  allocated, eight drives are used to make a four-drive RAID 0 array, which is then mirrored to a  four-drive array (4x4).  When a drive fails in a RAID 10 array, the DA rejects the failing drive and takes a hot spare  into the array synthesists. Data is then copied from the good drive to the hot spare drive. The  spare that is used is chosen based on a smart algorithm that looks at the location of the  spares and the size and location of the failed drive. Remember, a RAID 10 array is effectively  a RAID 0 array that is mirrored. Therefore, when a drive fails in one of the RAID 0 arrays, you  can rebuild the failed drive by reading the data from the equivalent drive in the other RAID 0  array. While this data copy is occurring, the DA can still service read and write requests to the array  from the hosts. Performance might degrade while the copy operation is in progress because  DA and switched network resources are used to rebuild the RAID. Because a good drive is  available, this effect is minimal. Read requests for data on the failed drive likely are not  affected because they are all directed to the good copy on the mirrored drive. Write  operations are not affected. 94  IBM DS8880 Architecture and Implementation Drive failure with RAID 10 RAID 10 implementation in DS8880 3.5.7 RAID 10 overview