HP Smart Array Controllers and basic RAID performance factors

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Abstract
RAID storage technology continues to make advancements in drives, storage interfaces, RAID controller technology, and
processing power. The features of the HP Smart Array Controller, the RAID level that you use, and drive technologies can
all affect overall RAID performance. This technology brief provides an overview of the basic factors affecting RAID
performance today.
Benefits of drive arrays
Drive arrays address several basic issues with drive-based storage:
• Drive arrays allow the creation of large storage volumes using multiple, smaller drives.
• Drive arrays increase the I/O capabilities and maximum throughput of the storage subsystem over that of individual
drives.
• Drive arrays increase the reliability of data storage by using redundancy techniques (RAID levels) to ensure that the
failure of one or more physical drives does not result in a permanent loss of data.
Factors that affect performance
Many variables influence the overall performance of drive arrays. The primary factors that influence performance are:
• RAID level
The processing that the RAID level requires for high-level and low-level read and write operations affects
performance.
• Array controller
The processor and memory required to manage and execute the RAID operations as well as the read and write cache
used to optimize read/write performance all influence performance.
• Number of drives in the drive array
The number of drives in an array incluences performance because the Smart Array controller can execute more read
and write operations in parallel.
• Drive performance
Drive throughput capability (MiB/s) influences RAID performance when performing random reads and writes
(I/Os per second or IOPS).
• Storage interface performance
Storage interface performance, including the protocols (SAS and SATA) and the speed of the physical links between
the drives and the controller (3 GiB/s or 6 GiB/s) are factors that affect performance.
Each of these variables influences RAID performance. In addition, depending on the type of storage operation, these
factors can determine the upper limit of the drive array’s performance in a particular application environment.
HP Smart Array Controller performance
The Smart Array controller includes a processor, cache, and device driver that all contribute to providing optimum RAID
performance.
Smart Array processor
The processor on the Smart Array controller manages the RAID system and transforms high-level read or write requests
from an application into the complex series of individual instructions for the drive array.
Its capabilities are particularly critical to complex RAID operations, particularly write operations for redundant RAID
modes, such as RAID 5 and RAID 6. Both RAID 5 and RAID 6 use mathematical XOR (Exclusive or) operations to calculate
parity data. Redundant parity data provides data recovery capability if a physical drive failure occurs. Because the