Dell H800, H700 manual RAID 1 Mirroring, Example of RAID Advantages of RAID

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Dell

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 improved performance because each drive in the virtual disk needs to handle only part of a read or write request. However, because none of the data is mirrored or backed up on parity drives, one drive failure makes the virtual disk inaccessible and the data is lost permanently.

Data 1

Data 2

Data 3

Data 4

Data 5

Data 6

Data 7

Data 8

Data 9

Data 10

Data 11

Data 12

Data 13

Data 14

Data 15

Data 16

Drive 0

Drive 1

Drive 2

Drive 3

Figure 4. Example of RAID 0

Advantages of RAID 0

∙I/O performance is greatly improved by spreading the I/O load across many channels and drives (best performance is achieved when data is striped across multiple channels with only one drive per channel)

∙No parity calculation overhead is involved

∙Very simple design

∙Easy to implement

Disadvantages of RAID 0

∙Not a "true" RAID because the failure of just one drive will result in all data in a virtual disk being lost

∙Should not be used for critical data unless another form of data redundancy is deployed

5.3.2RAID 1 (Mirroring)

RAID 1 is achieved through disk mirroring to ensure data reliability or a high degree of fault tolerance. In a RAID 1 configuration, the RAID management software instructs the subsystem's controller to store data redundantly across a number of the drives (mirrored set) in the virtual disk. See Figure 5.

In other words, if a disk fails, the mirrored drive takes over and functions as the primary drive.

DELL PERC H700 and H800 Technical Guide

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Contents Dell PowerEdge RAID Controller Cards March Table of Contents Tables Appendix aProduct Comparison OverviewPerc H700 Overview Perc H700 Integrated Additional Sled for PCIe SlotPerc H800 Overview Perc H700 ModularPerc H800 Adapter New Features 6Gb/s SAS SAS 2.0 Overview2 6Gb/s SAS Expectation Gb/s SAS SAS 2.0 Features1 6Gb/s SAS Performance Benefit over 3Gb/s SAS SAS Performance DetailsProduct Support Dell PowerEdge Server SupportPowerEdge Server Support with Perc H700 and Perc H800 Management Software SupportOperating System Support with Perc H700 and Perc H800 Drive SupportDrive Support Product Overview Perc H700 and Perc H800 FeaturesPerc H700 and Perc H800 Overview Power Management RAID Level CacheCade Reconfiguring Virtual DisksCut-Through IO Fault-Tolerance Features RAID Level MigrationNon-Volatile Cache Using Replace Member and Revertible Hot SparesAutomatic Replace Member with Predicted Failure Physical Disk Hot Swapping Battery Back-up of Controller CacheEnclosure Affinity Disk Migration Configuring and Managing Secured RAIDDisk Roaming Perc H700 and H800 Security Key and RAID ManagementVirtual Disk Write Cache Policies Virtual Disk Read Cache PoliciesAbout RAID RAID 0 Striped Virtual Disk without Fault ToleranceRAID Overview Advantages of RAIDRAID 1 Mirroring Example of RAID Advantages of RAIDRAID 5 Striping With Distributed Parity Example of RAID 1 MirroringRAID 6 Striping With Dual Distributed Parity DriveRAID 10 Striping over Mirrored Sets Example of RAID 6 Single Virtual Disk with 5 drivesRAID 50 Striping Across RAID Disadvantages of RAIDRAID 60 Striping Across RAID Example of RAID 50 5 + Advantages of RAIDExample of RAID 60 6 + Advantages of RAID Appendix A. Additional Resources Resource Contact Information and Descriptions
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