Maximizing Fault Tolerance
Keywords: Nytro SW UG

> Maximizing Fault Tolerance

> Fault tolerance is achieved through the ability to perform automatic and transparent rebuilds using hot spare drives and hot swaps. A hot spare drive is an unused online available drive that the Nytro controller card instantly plugs into the system when an active drive fails. After the hot spare is automatically moved into the RAID drive group, the failed drive is automatically rebuilt on the spare drive. The RAID drive group continues to handle requests while the rebuild occurs.

> A hot swap is the manual substitution of a replacement unit in a disk subsystem for a defective one, where the substitution can be performed while the subsystem is running hot swap drives. Auto-Rebuild in the WebBIOS Configuration Utility allows a failed drive to be replaced and automatically rebuilt by hot-swapping the drive in the same drive bay. The RAID drive group continues to handle requests while the rebuild occurs, providing a high degree of fault tolerance and zero downtime.

> Table 5. RAID Levels and Fault Tolerance

> RAID Level | Fault Tolerance
> 0 | Does not provide fault tolerance. All data is lost if any drive fails. Disk striping writes data across multiple drives instead of just one drive. It involves partitioning each drive storage space into stripes that can vary in size. RAID 0 is ideal for applications that require high performance but do not require fault tolerance.
> 1 | Provides complete data redundancy. If one drive fails, the contents of the other drive in the drive group can be used to run the system and reconstruct the failed drive. The primary advantage of disk mirroring is that it provides 100 percent data redundancy. Because the contents of the drive are completely written to a second drive, no data is lost if one of the drives fails. Both drives contain the same data at all times. RAID 1 is ideal for any application that requires fault tolerance and minimal capacity.
> 5 | Combines distributed parity with disk striping. Parity provides redundancy for one drive failure without duplicating the contents of entire drives. If a drive fails, the Nytro controller card uses the parity data to reconstruct all missing information. In RAID 5, this method is applied to entire drives or stripes across all drives in a drive group. Using distributed parity, RAID 5 offers fault tolerance with limited overhead.
> 10 | Provides complete data redundancy using striping across spanned RAID 1 drive groups. RAID 10 works well for any environment that requires the 100 percent redundancy offered by mirrored drive groups. RAID 10 can sustain a drive failure in each mirrored drive group and maintain data integrity.

DB15-001059-00-April 2013
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