Logical Subsystems - IBM DS8900F Introduction And Planning Manual

Usable capacity for the storage system can be configured as RAID 5, RAID 6, or RAID 10. RAID 6 can offer
excellent performance for some applications, while RAID 10 can offer better performance for selected
applications, in particular, high random, write content applications in the open systems environment.
RAID 6 increases data protection by adding an extra layer of parity over the RAID 5 implementation.
RAID 6 is the recommended and default RAID type for all drives over 1 TB. RAID 6 and RAID 10 are the
only supported RAID types for 1.92 TB Flash Tier 2 and 3.84 TB Flash Tier 1 drives. RAID 6 is the only
supported RAID type for 7.68 TB and 15.36 TB Flash Tier 2 drives.
Note: RAID 5 is not supported for drives larger than 1 TB and requires a request for price quote (RPQ). For
information, contact your sales representative.
RAID 5 overview
RAID 5 is a method of spreading volume data across multiple drives.
RAID 5 increases performance by supporting concurrent accesses to the multiple drives within each
logical volume. Data protection is provided by parity, which is stored throughout the drives in the array. If
a drive fails, the data on that drive can be restored using all the other drives in the array along with the
parity bits that were created when the data was stored.
RAID 5 is not supported for drives larger than 1 TB and requires a request for price quote (RPQ). For
information, contact your sales representative.
Note: RAID 6 is the recommended and default RAID type for all drives over 1 TB. RAID 6 and RAID 10 are
the only supported RAID types for 1.92 TB Flash Tier 2 and 3.84 TB Flash Tier 1 drives. RAID 6 is the only
supported RAID type for 7.68 TB and 15.36 TB Flash Tier 2 drives.
RAID 6 overview
RAID 6 is a method of increasing the data protection of arrays with volume data spread across multiple
disk drives.
RAID 6 increases data protection by adding an extra layer of parity over the RAID 5 implementation. By
adding this protection, RAID 6 can restore data from an array with up to two failed drives. The calculation
and storage of extra parity slightly reduces the capacity and performance compared to a RAID 5 array.
Note: RAID 6 is the recommended and default RAID type for all drives over 1 TB. RAID 6 and RAID 10 are
the only supported RAID types for 1.92 TB Flash Tier 2 and 3.84 TB Flash Tier 1 drives. RAID 6 is the only
supported RAID type for 7.68 TB and 15.36 TB Flash Tier 2 drives.
RAID 10 overview
RAID 10 provides high availability by combining features of RAID 0 and RAID 1.
RAID 0 increases performance by striping volume data across multiple disk drives. RAID 1 provides disk
mirroring, which duplicates data between two disk drives. By combining the features of RAID 0 and RAID
1, RAID 10 provides a second optimization for fault tolerance.
RAID 10 implementation provides data mirroring from one disk drive to another disk drive. RAID 10
stripes data across half of the disk drives in the RAID 10 configuration. The other half of the array mirrors
the first set of disk drives. Access to data is preserved if one disk in each mirrored pair remains available.
In some cases, RAID 10 offers faster data reads and writes than RAID 6 because it is not required to
manage parity. However, with half of the disk drives in the group used for data and the other half used to
mirror that data, RAID 10 arrays have less capacity than RAID 6 arrays.
Note: RAID 6 is the recommended and default RAID type for all drives over 1 TB. RAID 6 and RAID 10 are
the only supported RAID types for 1.92 TB Flash Tier 2 and 3.84 TB Flash Tier 1 drives. RAID 6 is the only
supported RAID type for 7.68 TB and 15.36 TB Flash Tier 2 drives.

Logical subsystems

To facilitate configuration of a storage system, volumes are partitioned into groups of volumes. Each
group is referred to as a logical subsystem (LSS).
As part of the storage configuration process, you can configure the maximum number of LSSs that you
plan to use. The storage system can contain up to 255 LSSs and each LSS can be connected to 16 other
16 IBM DS8900F: DS8900F Introduction and Planning Guide