Dell Precision 690 - Manual (Page 21)

About RAID Configurations
This section provides an overview of the RAID configuration that you might have selected when you purchased your computer. Although there are several RAID
configurations available in the computer industry for different types of uses, Dell offers RAID level 0, RAID level 1, or, with an optional PCI Express RAID
controller, RAID level 5 or RAID level 10 on your Dell Precision computer. A RAID level 0 configuration is recommended for high-performance programs, and a
RAID level 1 configuration is recommended for users that desire a high level of data integrity. A RAID level 5 or a RAID level 10 configuration provides for both
data integrity and higher access speeds.
The RAID controller on your computer can only create a RAID level 0 configuration using two to four physical drives. A RAID level 5 or 10 array (only available
with the optional PCI Express RAID controller) must be made up of three or four drives.
All drives must be the same type of drive; SAS and SATA drives cannot be mixed in a RAID array. The drives should also be the same size to ensure that the
larger drive does not contain unallocated (and therefore unusable) space.
RAID Level 0
RAID level 0 uses a storage technique known as "data striping" to provide a high data access rate. Data striping is a method of writing consecutive
segments—or stripes—of data sequentially across the physical drives to create a large virtual drive. Data striping allows one of the drives to read data while
the other drive is searching for and reading the next block.
Another advantage of a RAID level 0 configuration is that it utilizes the full capacities of the drives. If you have two 120-GB drives installed, you have 240 GB
on which to store data.
RAID Level 1
RAID level 1 uses a data-redundancy storage technique known as "mirroring." When data is written to the primary drive, the data is then duplicated—or
mirrored—on the other drive. A RAID level 1 configuration sacrifices high-data access rates for its data redundancy advantages.
If a drive failure occurs, subsequent read and write operations are directed to the surviving drive. A replacement drive can then be rebuilt using the data from
the surviving drive. Also, because data is duplicated on both drives, two 120-GB RAID level 1 drives collectively have a maximum of 120-GB on which to store
data.
NOTE: RAID levels 5 and 10 are only available via an optional PCI Express RAID controller card.
NOTE: RAID for SATA 1.0 is not supported.
NOTE: RAID levels do not represent a hierarchy. A RAID level 5 configuration is not inherently better or worse than a RAID level 0 configuration.
NOTE: RAID levels do not represent a hierarchy. A RAID level 10 configuration is not inherently better or worse than a RAID level 0 configuration.
NOTICE: Because RAID level 0 provides no data redundancy, if one drive fails, then the data on the other drive is also inaccessible. Therefore, ensure
that you perform regular backups when you use a RAID level 0 configuration.