Users Guide

NOTE: The maximum number of virtual disks is currently limited to 192, because of the supported enclosure configuration.

RAID terminology

Disk striping

Disk striping allows you to write data across multiple physical disks instead of just one physical disk. Disk striping involves

partitioning each physical disk storage space in stripes of the following sizes: 64 KB, 128 KB, 256 KB, 512 KB, and 1 MB. The

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 disk striping (used in RAID 0), segment 1 is written to disk 1, segment 2 is written

to disk 2, and so on. Disk striping enhances performance because multiple physical disks are accessed simultaneously, but disk

striping does not provide data redundancy.

Figure 21. Example of disk striping (RAID 0)

Disk mirroring

With mirroring (used in 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 disk mirroring is

that it provides complete data redundancy. Both disks contain the same data at all times. Either of the physical disks can act as

the operational physical disk.

Disk mirroring provides complete redundancy, but is an expensive option because each physical disk in the system must be

duplicated.

NOTE: Mirrored physical disks improve read performance by read load balance.

Figure 22. Example of Disk Mirroring (RAID 1)

Spanned RAID levels

Spanning is a term used to describe the way in which RAID levels 10, 50, and 60 are constructed from multiple sets of basic, or

simple RAID levels. For example, a RAID 10 has multiple sets of RAID 1 arrays where each RAID 1 set is considered a span. Data is

then striped (RAID 0) across the RAID 1 spans to create a RAID 10 virtual disk. Similarly, RAID 50 and RAID 60 combine multiple

sets of RAID 5 or RAID 6 respectively with striping.

Appendix RAID description