HP Smart Array Controller technology, 4th edition

RAID performance enhancements

Smart Array controllers use several enhancements to increase RAID performance.

Background RAID creation

When you create a RAID 1, RAID 5, or RAID 6 logical drive, the Smart Array controller must build the

logical drive within the array and initialize the parity before enabling certain advanced performance

techniques. Parity initialization takes several hours to complete. The time it takes depends on the size of the

logical drive and the load on the controller. The Smart Array controller creates the logical drive, initializing

the parity whenever the controller is not busy. While the controller creates the logical drive, you can access

the storage volume which has full fault tolerance.

RAID 5 and RAID 6 read-modify-write

After parity initialization is complete, writes to a RAID 5 or RAID 6 logical drive are typically faster because

the controller does not read the entire stripe to update the parity data. Since the controller knows that the

parity data is consistent with all the member drives in the stripe, the controller needs to read from only two

disk drives during a RAID 5 write or three disk drives for a RAID 6 write to compute the parity data,

regardless of array size.

Striping across arrays

RAID 50 and 60 methods stripe the data across multiple RAID/JBOD sets with different levels of parity.

These nested RAID types let you configure arrays across HP Modular Smart Arrays (MSAs).

RAID 50 (RAID 5+0) uses RAID 0 block-level striping across RAID 5 arrays with distributed parity. RAID 50

will tolerate one drive failure in each spanned array without loss of data. RAID 50 configurations require a

minimum of six drives and require less rebuild time than single RAID 5 arrays.

RAID 60 (RAID 6+0) uses RAID 0 block-level striping across multiple RAID 6 arrays with dual distributed

parity. With dual parity, RAID 60 will tolerate the failure of two disks in each spanned array without data

loss. RAID 60 configurations require a minimum of eight drives.

RAID 60 is available as an option with the Smart Array Advanced Pack

(see section later in this paper) and

is not supported on all HP Smart Array controllers.

RAID 1 load balancing

RAID 1 logical drives contain two copies of the data. During reads to RAID 1 logical drives, the Smart

Array controller issues read requests to either drive in the mirrored set. The Smart Array controller uses

RAID 1 load balancing to balance the number of requests between the two disk drives during a heavy read

load to achieve higher read bandwidth.

Data availability

Smart Array controllers support online array expansion, logical drive extension, strip

size migration, and

RAID migration. These technologies protect data and let you modify the array without interrupting data

access. Smart Array controllers can monitor I/O activity, track key parameters, predict potential problems,

When a Smart Array controller makes an array, the unit of data that it manipulates is defined as a “strip” (ranging in size from 64

KiB to 256 KiB). These strips are distributed across the physical drives in the array. A "stripe" is one set of strips. Our Smart Array

controllers actually configure strips not stripes. You can calculate the stripe size from the strip size, the number of physical drives in

the logical drive, and the RAID level.