Intel SRCU31 user manual RAID Levels Examples, Striping

RAID Features

typically exhibit irregular patterns of write intensity over time. Such applications normally write short bursts of data. Such applications may include transaction processing (perhaps sorting applications or accounting software). Also, enabling the write-cache will usually improve sequential write performance for RAID-5 volumes.

Some applications may incur some performance degradation with the write-cache enabled. Example applications would include video editing, graphics intensive applications, video streaming, or other applications which access or copy large files. It is recommended that the user try both modes of operation (cache enabled and cache disabled) to determine which mode operation provides the best performance for the applications that are commonly used.

5.2.9RAID Levels Examples

5.2.9.1Striping

Disk striping is the interleaving of data across multiple drives in an array. Data is sequentially stored in allocated sizes, based on the RAID level. Striping improves performance because it makes data available for reading and writing on multiple disks simultaneously. See Table 5-1for more information on RAID levels and the level of performance and protection they offer.

Strip size refers to the allocated space on a disk. Stripe size is the number of drives x the strip size. For example, 4 drives x a strip size of 64k is equal to a stripe size of 256k in a Raid level 5 configuration. Figure 5-2illustrates how data is striped across a group of disks. Strip size is specified when you create a RAID volume.

Figure 5-2. Stripes and Strips in a RAID Volume

Disk #0 Disk #1 Disk #2 Disk #3

D16	D17	D18	D19
D12	D13	D14	D15
D8	D9	D10	D11
D4	D5	D6	D7
D0	D1	D2	D3

Strips D0, D1, D2 and D3 constitute the first stripe in Volume 0. Strip size is specified when you create a RAID volume.

Vol 1

Vol 0

5-14 Intel® Server RAID Controller U3-1 User’s Manual Rev 1.0