PowerEdge - What are the different RAID levels and their specifications

Allows you to write data across multiple hard drives instead of one hard drive RAID 0 partitions each hard drive storage space into 64 KB stripes. These stripes are interleaved in a repeated sequential manner. The part of the stripe on a single hard drive is called a stripe element.
For example, in a four-disk system using only RAID 0, segment 1 is written to disk 1, segment 2 is written to disk 2, and so on. RAID 0 enhances performance because multiple hard drives are accessed simultaneously, but it does not provide data redundancy (Figure 1 (English only)).

Figure 1: RAID 0

• Fault Tolerance - None
• Advantage - Improved performance, extra storage
• Disadvantage - Should not be used for critical data Data Loss occurs with any drive failure.

With RAID 1, data written to one disk is simultaneously written to another disk. If one disk fails, the contents of the other disk can be used to run the system and rebuild the failed hard drive. 
The primary advantage of RAID 1 is that it provides 100 percent data redundancy. Because the contents of the disk are written to a second disk, the system can sustain the failure of one disk. Both disks contain the same data always. Either hard drive can act as the operational hard drive (Figure 2 (English only)).

 

Figure 2: RAID 1

• Fault Tolerance - Disk errors, Single disk failure
• Advantage - High read performance, Fast recovery after drive failure, Data redundancy
• Disadvantage - High disk overhead, Limited capacity

RAID 5 and 6: Parity Data is redundant data that is generated to provide fault tolerance within certain RAID levels. When a drive failure occurs, the controller uses the parity data to regenerate user data.
Parity data is present for RAID 5, 6, 50, and 60. The parity data is distributed across all the hard drives in the system. If a single hard drive fails, it can be rebuilt from the parity and the data on the remaining hard drives.

• RAID level 5 combines distributed parity with disk striping, as shown below (Figure 3 (English only)). Parity provides redundancy for one hard drive failure without duplicating the contents of entire hard drives.
• RAID 6 combines dual distributed parity with disk striping (Figure 4 (English only)). This level of parity allows for two disk failures without duplicating the contents of entire hard drives.

 
RAID 5
 

Figure 3: RAID 5

• Fault Tolerance - Disk errors, Single disk failures
• Advantage - Efficient use of drive capacity, High read performance, Med-to-High write performance
• Disadvantage - Disk failure medium impact, Longer re-build due to parity re-calculation

RAID 6
 

Figure 4: RAID 6

• Fault Tolerance - Disk errors, Dual disk failures
• Advantage - Data redundancy, High read performance
• Disadvantage - Write performance decrease due to dual parity calculations, Extra cost due to two disk equivalent devoted to parity

RAID 10: RAID 10 requires two or more mirrored sets working together. Multiple RAID 1 sets are combined to form a single array. Data is striped across all mirrored drives. 
Since each drive is mirrored in RAID 10, no delay is encountered because no parity calculation is done. 
This RAID strategy can tolerate the loss of multiple drives as long as two drives of the same mirrored pair do not fail. RAID 10 volumes provide high data throughput and complete data redundancy (Figure 5 (English only)).
 

Figure 5: RAID 10

• Fault Tolerance - Disk errors, One disk failure per mirrored set
• Advantage - High read performance, Supports largest RAID group of 192 drives
• Disadvantage - Most expensive