RAID Product Options

The following sections briefly discuss several ways to implement RAID.

Host Volume Managers

Host volume management software typically has several RAID variations and, in some cases, offers many sophisticated configuration options. Running RAID in a volume manager opens the potential for integrating file system and volume management products for management and performance-tuning purposes. Another advantage of using host volume management is the ability to use less expensive just a bunch of disks (JBOD) disk subsystems, as opposed to expensive disk subsystems.

The performance impact of RAID on the host CPU is often overestimated, because the address space translation process for striping data is a relatively low overhead process. However, the element of RAID that is time-consuming is the reading and writing of data in RAID 5 operations. This highlights another subtle advantage of RAID 10 over RAID 5. RAID 10 only performs Boolean operations, and avoids slow read and write operations.

RAID on Motherboard (ROM)

RAID on motherboard (ROM) has not been used much in storage networks, but that could change over time. The idea of ROM is that a chipset on the system board provides the core RAID functionality that is used for motherboard-integrated storage I/O communications adapters. In general, ROM does not have nearly the flexibility and power of volume management software, but it can work reasonably well for limited environments, smaller storage networks, and inexpensive storage subsystems or JBOD. In the future, this will include combinations of Fibre Channel (FC), iSCSI, and Serial ATA (SATA)/Serial Attached SCSI (SAS).

Host Bus Adapters

RAID has been implemented in adapters/controllers for many years, starting with SCSI and including Advanced Technology Attachment (ATA) and serial ATA. RAID on FC HBAs has not been implemented yet, but there is no reason to believe it won't be in the years to come. The operating environment for HBA RAID is similar to ROMsmaller storage networks and inexpensive subsystems or JBOD.

Disk Subsystems

Disk subsystems have been the most popular product for RAID implementations and probably will continue to be for many years to come. There is an enormous range of capabilities offered in disk subsystems across a wide range of prices. Chapter 5 discusses these important products in much more detail.

Network Systems

Finally, RAID capabilities have been introduced in networking equipment, such as switches and specialized storage appliances. In general, most RAID applications in networking equipment are made for enterprise environments and involve technologies ported from volume management software or enterprise subsystem controllers.