Striping Across Arrays; Raid 1 Load Balancing; Hardware Versus Software Raid - HP 273914-B21 - Smart Array 6404/256 RAID Controller Technology Brief

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 allow users to configure arrays across HP Modular Smart Arrays
(MSAs).
RAID 50 (RAID 5+0) is a nested RAID method that 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) is a nested RAID method that uses RAID 0 block-level striping across multiple
RAID 6 arrays with dual distributed parity. With the inclusion of 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 6 and 60 are available as an option with the Smart Array Advanced Pack (see section later in
this paper) and are not supported on all HP Smart Array controllers.

RAID 1 load balancing

In general, the same stripe and array sizes, RAID 0, RAID 5, and RAID 6, have the same read
performance. 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. During a
heavy read load, the Smart Array controller balances the number of requests between the two disk
drives to achieve higher read bandwidth. This technique is called RAID 1 load balancing.

Hardware versus software RAID

Today's operating systems offer basic support for RAID 0, RAID 1, and RAID 5 disks (called software
RAID) to create and manage logical drives that do not contain the operating system. Software RAID
requires a significant amount of the server's resources to perform management functions. However,
Smart Array controllers use a separate processor and memory subsystem for management functions.
Furthermore, with Smart Array controllers, the parity calculations required by RAID 5 and RAID 6 are
performed by specialized hardware engines that maximize data throughput for disk write, rebuild,
and regenerate read operations.
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