Avago Technologies MegaRAID Fast Path Software - Manual (Page 42)

Page 42 LSI Corporation Confidential | July 2011
MegaRAID SAS Software User Guide Chapter 2: Introduction to RAID | RAID Configuration Strategies
2.6.2 Maximizing Performance A RAID disk subsystem improves I/O performance. The RAID drive group appears to the
host computer as a single storage unit or as multiple virtual units. I/O is faster because
drives can be accessed simultaneously.
Table 16 describes the performance for each
RAID level.
10 Provides complete data redundancy using striping across spanned RAID 1 drive groups. RAID 10 works well for any environment that
requires the 100 percent redundancy offered by mirrored drive groups. RAID 10 can sustain a drive failure in each mirrored drive group
and maintain data integrity.
50 Provides data redundancy using distributed parity across spanned RAID 5 drive groups. RAID 50 includes both parity and disk striping
across multiple drives. If a drive fails, the RAID controller uses the parity data to re-create all missing information. RAID 50 can sustain
one drive failure per RAID 5 drive group and still maintain data integrity.
60 Provides data redundancy using distributed parity across spanned RAID 6 drive groups. RAID 60 can sustain two drive failures per RAID
6 drive group and still maintain data integrity. It provides the highest level of protection against drive failures of all of the RAID levels.
RAID 60 includes both parity and disk striping across multiple drives. If a drive fails, the RAID controller uses the parity data to re-create
all missing information.
Table 15: RAID Levels and Fault Tolerance (Continued)
RAID
Level
Fault Tolerance
Table 16: 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.
Because 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.