Disk Mirroring

With mirroring (used in 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 physical disk. The primary advantage of disk mirroring is that it provides complete data redundancy. Both disks contain the same data at all times. Either of the physical disks can act as the operational physical disk.

Disk mirroring provides complete redundancy, but is an expensive option because each physical disk in the system must be duplicated.

NOTE: Mirrored physical disks improve read performance by read load balance.

Figure A-2 shows an example of disk mirroring.

Figure A-2. Example of Disk Mirroring (RAID 1)

Stripe element 1 Stripe element 1 Duplicated

Stripe element 2 Stripe element 2 Duplicated

Stripe element 3 Stripe element 3 Duplicated

Stripe element 4 Stripe element 4 Duplicated

Spanned RAID Levels

Spanning is a term used to describe the way in which RAID levels 10, 50, and 60 are constructed from multiple sets of basic, or simple RAID levels. For example, a RAID 10 has multiple sets of RAID 1 arrays where each RAID 1 set is considered a span. Data is then striped (RAID 0) across the RAID 1 spans to create a RAID 10 virtual disk. Similarly, RAID 50 and RAID 60 combine multiple sets of RAID 5 or RAID 6 respectively with striping.

Parity Data

Parity data is redundant data that is generated to provide fault tolerance within certain RAID levels. In the event of a disk failure the parity data can be used by the controller to regenerate user data. Parity data is present for RAID 5, 6, 50, and 60.

Appendix: RAID Description

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H310, H710, H710P, H810 specifications

Dell offers a range of storage controller technologies, notably the H810, H710, H710P, and H310, which cater to different enterprise needs. These controllers are designed to support various storage configurations, enhancing overall system performance and reliability.

The Dell H810 is a high-performance PCIe 3.0 RAID controller that supports up to eight internal drives and is particularly suited for demanding workloads. It features advanced RAID levels including RAID 0, 1, 5, 6, 10, 50, and 60, providing flexibility for various data protection strategies. The H810 also supports up to 32TB of storage capacity, making it suitable for environments that require substantial data management capabilities.

The H710 is another powerful RAID controller, widely recognized for its balance of performance and cost-efficiency. It features 1GB of cache memory, which aids in accelerating read and write operations. The H710 supports the same RAID levels as the H810 and allows for up to 512MB of non-volatile memory. This ensures data integrity even in the event of a power failure, making it reliable for critical applications.

The H710P is an enhanced version of the H710, with a significant upgrade in its cache capabilities. It offers 2GB of battery-backed cache memory, further enhancing data processing speeds and improving responsiveness. The H710P is ideal for intensive workloads and virtualization, where rapid access to data is essential. This controller also includes features such as RAID storage pooling, intelligent data tiering, and support for multiple virtual disks.

Finally, the H310 is a cost-effective option for small to medium-sized businesses or those with less demanding storage requirements. It offers similar RAID support as the higher-end controllers but operates with a simpler architecture. The H310 features 512MB of cache, providing sufficient performance for regular workloads without the additional complexities of more advanced controllers.

In summary, Dell's H810, H710, H710P, and H310 storage controllers each serve distinct purposes, providing various features, technologies, and performance characteristics tailored to different business needs. From high-capacity storage solutions to user-friendly setups, Dell’s offerings ensure that organizations can efficiently manage their data storage requirements.