Dell PERC 4/SI - Manual (Page 12)

Disk striping allows you to write data across multiple physical disks instead of just one physical disk. Disk striping involves partitioning each drive storage
space into stripes that can vary in size from 8 KB to 128 KB. These stripes are interleaved in a repeated sequential manner. The combined storage space is
composed of stripes from each drive. PERC 4/Di/Si and 4e/Di/Si support stripe sizes of 2 KB, 4 KB, 8 KB, 16 KB, 32 KB, 64 KB, and 128 KB. It is recommended
that you keep stripe sizes the same across RAID arrays.
For example, in a four-disk system using only disk striping (used in RAID level 0), segment 1 is written to disk 1, segment 2 is written to disk 2, and so on. Disk
striping enhances performance because multiple drives are accessed simultaneously, but disk striping does not provide data redundancy.
Figure 2 -1 shows an example of disk striping.
Figure 2-1. Example of Disk Striping (RAID 0)
Stripe Width
Stripe width is the number of disks involved in an array where striping is implemented. For example, a four-disk array with disk striping has a stripe width of
four.
Stripe Size
The stripe size is the length of the interleaved data segments that the RAID controller writes across multiple drives. PERC 4/Di/Si and 4e/Di/Si support stripe
sizes of 2 KB, 4 KB, 8 KB, 16 KB, 32 KB, 64 KB, and 128 KB.
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 reconstruct the failed disk. The primary advantage of disk mirroring is that it provides 100% 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 drive can act
as the operational drive.
Disk mirroring provides 100% redundancy, but is expensive because each drive in the system must be duplicated. Figure 2 -2 shows an example of disk
mirroring.
Figure 2-2. Example of Disk Mirroring (RAID 1)
Parity
NOTE: Using a 2 KB or 4 KB stripe size is not recommended due to performance implications. Use 2 KB or 4 KB only when required by the applications
used. The default stripe size is 64 KB. Do not install an operating system on a logical drive with less than a 16 KB stripe size.
NOTE: Using a 2 KB or 4 KB stripe size is not recommended due to performance implications. Use 2 KB or 4 KB only when required by the applications
used. The default stripe size is 64 KB. Do not install an operating system on a logical drive with less than a 16 KB stripe size.