5-14 Intel® Server RAID Controller U3-1 User’s Manual Rev 1.0
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.
5.2.9 RAID Levels Examples
5.2.9.1 Striping
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 5-1 for
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 5-2 illustrates 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
Vol 1
Vol 0
Strips D0, D1, D2 and D3 constitute the first stripe in Volume 0. Strip size is
specified when you create a RAID volume.
D16
D12
D8
D4
D0
D17
D13
D9
D5
D1
D18
D14
D10
D6
D2
D19
D15
D11
D7
D3
