Dell Perc 6i Manual

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5 RAID Overview 
5.1 About RAID 
RAID is a way of storing data on multiple independent physical disks for the purpose of enhanced 
performance and/or fault tolerance. The physical disks combine to make up what is called a virtual 
disk. This virtual disk appears to the host system as a single logical unit or drive. For example, if you 
have physical disk 1 and physical disk 2 forming a RAID virtual disk, those two disks appear to the 
host system as one...

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For example, a four-drive virtual disk may be configured with 16 stripes (four stripes of designated 
space per drive). Stripes A, B, C and D are located on corresponding hard drives 0, 1, 2, and 3. Stripe 
E, however, appears on a segment of drive 0 in a different location than stripe A; stripes F through H 
appear accordingly on drives 1, 2 and 3. The remaining eight stripes are allocated in the same even 
fashion across the drives. 
 
RAID 0 provides...

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Figure 5. Example of RAID 1 (Mirroring) 
Advantages of RAID 1 
 High performance up to twice the read transaction rate of single disks, and the same write 
transaction rate as single disks  
 100 percent redundancy of data means no rebuild of data is necessary in case of disk failure, 
just a copy to the replacement disk 
 Typically supports hot-swap disks  
 Simplest RAID storage...

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Figure 6. Example of RAID 5 (Single Virtual Disk with 5 drives) 
Advantages of RAID 5 
 Most efficient use of drive capacity of all the redundant RAID configurations 
 High read transaction rate 
 Medium-to-high write transaction rate 
Disadvantages of RAID 5  
 Disk failure has a medium impact on throughput 
 Most complex controller design 
 Retrieval of...

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Figure 7. Example of RAID 6 (Single Virtual Disk with 5 drives) 
Advantages of RAID 6 
 Can survive the loss of two disks without losing data 
 Data redundancy, high read rates, and good performance 
Disadvantages of RAID 6  
 Requires two sets of parity data for each write operation, resulting in significant decrease in 
write performance 
 Additional costs because of the...

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Figure 8. Example of RAID 10 (1 + 0) 
Advantages of RAID 10 
 RAID 10 has the same redundancy as RAID level 1 
 High I/O rates are achieved by striping RAID 1 segments 
 Allows creation of largest RAID group with up to 192 drives connected to PERC H800 
Disadvantages of RAID 10 
 Most expensive RAID solution 
 Requires 2n where n > 1 disks 
5.3.6 RAID 50 (Striping Across RAID 5) 
RAID 50 is a variation of RAID 5...

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Figure 9. Example of RAID 50 (5 + 0) 
Advantages of RAID 50 
 Allows creation of largest RAID groups, up to 256 drives (theoretical; large RAID volumes are 
allowed for up to 192 drives connected to PERC H800) 
 High read transaction rate 
 Higher degree of fault tolerance due to parity calculation being done for each RAID 5 subset 
 Potential for faster read transaction rates over large RAID 5 virtual disks 
 Medium-to-high write transaction...

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Figure 10. Example of RAID 60 (6 + 0) 
Advantages of RAID 60 
 Allows creation of largest RAID groups, up to 256 drives (theoretical); large RAID volumes are 
allowed for up to 192 drives connected to PERC H800 
 High degree of fault tolerance due to 2 parity calculations being done for each RAID 6 subset 
 Medium-to-high write transaction rate 
Disadvantages of RAID 60  
 One of the more complex RAID implementations 
 Less space-efficient...

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DELL PERC H700 and H800 Technical Guide   29 
Appendix A. Additional Resources 
Table 9. Resource Contact Information and Descriptions 
Type Of Information URL Description 
PERC Resources http://www.dell.com/PERC   
 
Support matrix, whitepapers, 
and important links 
 
PERC Hardware 
Owner’s Manual 
http://support.dell.com/manuals Specifications, feature 
overview and descriptions, 
installation, management, and 
troubleshooting 
 
OpenManage User 
Documentation 
http://www.support.dell.com/...