Dell PERC S300, (PERC) S100 manual Spanned RAID Levels, Parity Data

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

NOTE: The PERC S300 controller only supports physical disks (SAS and SATA). SSD devices cannot be migrated to a PERC S300 controller.

Figure 2-2. 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 level 10 is constructed from multiple sets of simpler RAID levels. For example, a RAID 10 has multiple sets of RAID 1 disk arrays in which each RAID 1 set is considered a span. Data is then striped (as it is in RAID 0) across the RAID 1 spans to create a RAID 10 virtual disk.

Parity Data

Parity data is redundant data that has been generated to provide fault tolerance within certain RAID levels. In the event of a drive failure, the parity data can be used by the controller to regenerate user data. Parity data is present only for RAID 5 disk arrays.

The parity data is distributed across all the physical disks in the system. If a single physical disk fails, it can be rebuilt from the parity and the data on the remaining physical disks. RAID 5 combines distributed parity with disk striping, as shown in Figure 2-3. Parity provides redundancy for one physical disk failure without duplicating the contents of entire physical disks.

Overview

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