PERC 2/DC also supports independent drives (configured as RAID 0.)
Select a RAID LevelTo ensure the best performance, you should select the optimal RAID level when you create a system drive. The optimal RAID level for your disk array depends on a number of factors:
|
|
Level |
Use |
Pros |
Cons |
Max. Drives |
Fault Tolerant |
|
0 |
Data divided in blocks and distributed sequentially (pure striping). Use for non-critical data that requires high performance. |
High data throughput for large files |
No fault tolerance. All data lost if any drive fails. |
1 to 8 |
No |
|
1 |
Data duplicated on another disk (mirroring). Use for read-intensive fault-tolerant systems |
100% data redundancy |
Doubles disk space. Reduced performance during rebuilds. |
2, 4, 6, or 8 |
Yes |
|
5 |
Disk striping and parity data across all drives. Use for high read volume but low write volume, such as transaction processing. |
Achieves data redundancy at low cost |
Write performance not as good as RAID 1 |
3 to 8 |
Yes |
|
10 (1 + 0) |
A combination of data mirroring and data striping |
Higher performance, higher capacity, and 100% redundancy |
Higher cost |
4 to 16 |
Yes |
|
50 (5 + 0) |
A combination of disk striping and striping with parity |
Higher capacity array |
Same as RAID 5 |
6 to 16 |
Yes |
RAID 0 provides disk striping across all drives in the RAID subsystem. RAID 0 does not provide any data redundancy, but does offer the best performance of any RAID level. RAID 0 breaks up data into smaller blocks and then writes a block to each drive in the array. The size of each block is determined by the stripe size parameter, set during the creation of the RAID set. RAID 0 offers high bandwidth. By breaking up a large file into smaller blocks, PERC 2/DC can use several drives to read or write the file faster. RAID 0 involves no parity calculations to complicate the write operation. This makes RAID 0 ideal for applications that require high bandwidth but do not require fault tolerance. RAID 0 is also used to denote an independent or single drive.
Table 3. RAID 0 Summary
|
Uses |
RAID 0 provides high data throughput, especially for large files. Any environment that does not require fault tolerance. |
|
Strong Points |
Provides increased data throughput for large files. No capacity loss penalty for parity. |
|
Weak Points |
Does not provide fault tolerance. All data lost if any drive fails. |
|
Drives |
1 to 8 |
Figure 1. RAID 0
In RAID 1, PERC 2/DC duplicates all data from one drive to a second drive. RAID 1 provides complete data redundancy, but at the cost of doubling the required data storage capacity.
Table 4. RAID 1 Summary
|
Uses |
Use RAID 1 for small databases or any other environment that requires fault tolerance but small capacity. |
|
Strong Points |
RAID 1 provides complete data redundancy. RAID 1 is ideal for any application that requires fault tolerance and minimal capacity. |
|
Weak Points |
RAID 1 requires twice as many disk drives. Performance is impaired during drive rebuilds. |
|
Drives |
2 drives |
Figure 2. RAID 1
RAID 5 includes disk striping at the block level and parity. In RAID 5, the parity information is written to several drives. RAID 5 is best suited for networks that perform a lot of small input/output (I/O) transactions simultaneously.
RAID 5 addresses the bottleneck issue for random I/O operations. 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.
Table 5. RAID 5 Summary
|
Uses |
RAID 5 provides high data throughput, especially for large files. Use RAID 5 for transaction processing applications because each drive can read and write independently. If a drive fails, PERC 2/DC uses the parity drive to recreate all missing information. Use also for office automation and 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 and good performance in most environments. |
|
Weak Points |
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 8 |
Figure 3. RAID 5
RAID 10 is a combination of RAID 0 and RAID 1. RAID 10 has mirrored drives. RAID 10 breaks up data into smaller blocks, then stripes 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 striped size parameter, which is set during the creation of the RAID set. RAID 10 can sustain one to four drive failures while maintaining data integrity if each failed disk is in a different RAID 1 array.
Table 6. RAID 10 Summary
|
Uses |
RAID 10 works best for data storage that must have 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 |
RAID 10 provides both high data transfer rates and complete data redundancy. |
|
Weak Points |
RAID 10 requires twice as many drives as all other RAID levels except RAID 1. |
|
Drives |
2n, where n is greater than 1. |
Figure 5. RAID 10
RAID 50 provides the features of both RAID 0 and RAID 5. RAID 50 includes both parity and disk striping across multiple drives. 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 raid 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 50 can sustain one to four drive failures while maintaining data integrity if each failed disk is in a different RAID 5 array.
Table 7. RAID 50 Summary
|
Uses |
RAID 50 works best when used with data that requires high reliability, high request rates, high data transfer, and medium to large capacity. |
|
Strong Points |
RAID 50 provides high data throughout, data redundancy, and very good performance. |
|
Weak Points |
Requires 2 to 4 times as many parity drives as RAID 5. |
|
Drives |
6 to 16 |
Figure 6. RAID 50
