Dell PERC 4/SI - Manual (Page 18)

RAID 10
RAID 10 is a combination of RAID 0 and RAID 1. RAID 10 consists of stripes across mirrored drives. RAID 10 breaks up data into smaller blocks, then mirrors the
blocks of data to each RAID 1 RAID set. Each RAID 1 RAID set then duplicates its data to its other drive. The size of each block is determined by the stripe size
parameter, which is set during the creation of the RAID set. Up to 8 spans can be supported by RAID 10.
Table 2 -8 provides an overview of RAID 10.
Table 2-8. RAID 10 Overview
In Figure 2 -5 , logical drive 0 is created by distributing data across four arrays (arrays 0 through 3). Spanning is used because one logical drive is defined
across more than one array. Logical drives defined across multiple RAID 1 level arrays are referred to as RAID level 10, (1+0). To increase performance, by
enabling access to multiple arrays simultaneously, data is striped across arrays.
Using RAID level 10, rather than a simple RAID set, up to 8 spans can be supported, and up to 8 drive failures (one failure per span) can be tolerated, though
less than total disk drive capacity is available. Though multiple drive failures can be tolerated, only one drive failure can be tolerated in each RAID 1 level array.
Figure 2-5. RAID 10 Level Logical Drive
RAID 50
RAID 50 provides the features of both RAID 0 and RAID 5. RAID 50 includes both parity and disk striping across multiple arrays. RAID 50 is best implemented on
two RAID 5 disk arrays with data striped across both disk arrays.
RAID 50 breaks up data into smaller blocks, then stripes the blocks of data to each RAID 5 disk set. RAID 5 breaks up data into smaller blocks, calculates parity
by performing an exclusive-or on the blocks, then writes the blocks of data and parity to each drive in the array. The size of each block is determined by the
stripe size parameter, which is set during the creation of the RAID set.
RAID level 50 can support up to 8 spans and tolerate up to 8 drive failures (one failure per span), though less than total disk drive capacity is available.
Though multiple drive failures can be tolerated, only one drive failure can be tolerated in each RAID 1 level array.
online customer service that requires fault tolerance. Use for any application that has high read request rates but low write request rates.
Strong
Points Provides data redundancy, high read rates, and good performance in most environments. Provides redundancy with lowest loss of capacity.
Weak
Points Not well suited to tasks requiring lot of writes. Suffers more impact if no cache is used (clustering). Disk drive performance will be reduced if a
drive is being rebuilt. Environments with few processes do not perform as well because the RAID overhead is not offset by the performance gains
in handling simultaneous processes.
Drives 3 to 28
Uses Appropriate when used with data storage that needs 100% redundancy of mirrored arrays and that also needs the enhanced I/O performance
of RAID 0 (striped arrays.) RAID 10 works well for medium-sized databases or any environment that requires a higher degree of fault tolerance
and moderate to medium capacity.
Strong
Points Provides both high data transfer rates and complete data redundancy.
Weak
Points Requires twice as many drives as all other RAID levels except RAID 1.
Drives 2n, where n is greater than 1.