Lenovo ThinkServer RD230, Software User'S Manual

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2-30 Introduction to RAID
Table 2.14 RAID Levels and Performance
RAID
Level
Performance
0 RAID 0 (striping) offers excellent performance. RAID 0 breaks up data into smaller
blocks and then writes a block to each drive in the drive group. Disk striping writes data
across multiple drives instead of just one drive. It involves partitioning each drive
storage space into stripes that can vary in size from 8 KB to 1024 KB. These stripes
are interleaved in a repeated sequential manner. Disk striping enhances performance
because multiple drives are accessed simultaneously.
1 With RAID 1 (mirroring), each drive in the system must be duplicated, which requires
more time and resources than striping. Performance is impaired during drive rebuilds.
5 RAID 5 provides high data throughput, especially for large files. Use this RAID level for
any application that requires high read request rates, but low write request rates, such
as transaction processing applications, because each drive can read and write
independently. Since each drive contains both data and parity, numerous writes can
take place concurrently. In addition, robust caching algorithms and hardware based
exclusive-or assist make RAID 5 performance exceptional in many different
environments.
Parity generation can slow the write process, making write performance significantly
lower for RAID 5 than for RAID 0 or RAID 1. Drive performance is reduced when a drive
is being rebuilt. Clustering can also reduce drive performance. Environments with few
processes do not perform as well because the RAID overhead is not offset by the
performance gains in handling simultaneous processes.
6 RAID 6 works best when used with data that requires high reliability, high request rates,
and high data transfer. It provides high data throughput, data redundancy, and very
good performance. However, RAID 6 is not well suited to tasks requiring a lot of writes.
A RAID 6 virtual drive has to generate two sets of parity data for each write operation,
which results in a significant decrease in performance during writes. Drive performance
is reduced during a drive rebuild. Environments with few processes do not perform as
well because the RAID overhead is not offset by the performance gains in handling
simultaneous processes.
00 RAID 00 (striping in a spanned drive group) offers excellent performance. RAID 00
breaks up data into smaller blocks and then writes a block to each drive in the drive
groups. Disk striping writes data across multiple drives instead of just one drive. Striping
involves partitioning each drive storage space into stripes that can vary in size from
8 KB to 1024 KB. These stripes are interleaved in a repeated sequential manner. Disk
striping enhances performance because multiple drives are accessed simultaneously.
10 RAID 10 works best for data storage that need the enhanced I/O performance of
RAID 0 (striped drive groups), which provides high data transfer rates. Spanning
increases the capacity of the virtual drive and improves performance by doubling the
number of spindles. The system performance improves as the number of spans
increases. (The maximum number of spans is eight.) As the storage space in the spans
is filled, the system stripes data over fewer and fewer spans and RAID performance
degrades to that of a RAID 1 or RAID 5 drive group.