The Dell™ Serial-Attached SCSI (SAS) 5/iR controller is Dell's next generation of controller with integrated redundant array of independent disks (RAID) capabilities. SAS technology is not backward compatible with the previous generation of SCSI devices. The SAS 5/iR Adapter is a half-length, standard-height PCI-E card, while the SAS 5/iR Integrated is embedded in the platform hardware. The SAS 5/iR Adapter is supported on platforms with PCI-E x8 or x16 connectors.
Figure 1-1. SAS 5/iR Adapter Hardware Architecture
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SAS x4 internal connector
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PCI-E connector
About RAID
RAID is a group of multiple independent physical disks that provide high performance by increasing the number of drives used for saving and accessing data. A RAID disk subsystem improves I/O performance and data availability. The physical disk group appears to the host system as a single storage unit or as multiple logical units. Data throughput improves because multiple disks can be accessed simultaneously. RAID systems also improve data storage availability and fault tolerance.
RAID Levels
Integrated Striping or RAID 0 uses disk striping to provide high data throughput, especially for large files in an environment that requires no data redundancy.
Integrated Mirroring or RAID 1 uses disk mirroring so that data written to one physical disk is simultaneously written to another physical disk. This is good for small databases or other applications that require small capacity, but complete data redundancy.
NOTICE: Lost data on an Integrated Striping virtual disk cannot be recovered in the event of a physical disk failure.
RAID Terminology
Integrated Striping
Integrated Striping (RAID 0) allows you to write data across multiple physical disks instead of just one physical disk. Integrated Striping involves partitioning each physical disk storage space into 64 KB stripes. These stripes are interleaved in a repeated sequential manner. The part of the stripe on a single physical disk is called a stripe element.
For example, in a four-disk system using only Integrated Striping, segment 1 is written to disk 1, segment 2 is written to disk 2, and so on. Integrated Striping enhances performance because multiple physical disks are accessed simultaneously, but Integrated Striping does not provide data redundancy. Figure 1-2 shows an example of Integrated Striping.
Figure 1-2. Example of Integrated Striping (RAID 0)
Integrated Mirroring
With Integrated Mirroring (RAID 1), data written to one disk is simultaneously written to another disk. If one disk fails, the contents of the other disk can be used to run the system and rebuild the failed physical disk. The primary advantage of Integrated Mirroring is that it provides 100 percent data redundancy. Because the contents of the disk are completely written to a second disk, it does not matter if one of the disks fails. Both disks contain the same data at all times. Either physical disk can act as the operational physical disk.
