RAID Availability Concept
Keywords: Nytro SW UG

> RAID Availability Concept

> Data availability without downtime is essential for many types of data processing and storage systems. Businesses want to avoid the financial costs and customer frustration associated with failed servers. RAID helps you maintain data availability and avoid downtime for the servers that provide that data. RAID offers several features, such as spare drives and rebuilds, that you can use to fix any drive problems, while keeping the servers running and data available. The following subsections describe these features.

> Spare Drives

> You can use spare drives to replace failed or defective drives in a drive group. A replacement drive must be at least as large as the drive it replaces. Spare drives include hot swaps, hot spares, and cold swaps.

> 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 (performing its normal functions). The backplane must support hot swap in order for the functionality to work.

> Hot spare drives are drives that power up along with the RAID drives and operate in a Standby state. If a drive used in a RAID virtual drive fails, a hot spare automatically takes its place, and the data on the failed drive is rebuilt on the hot spare. Hot spares can be used for RAID 1, RAID 5, and RAID 10.

> NOTE If a rebuild to a hot spare fails for any reason, the hot spare drive is marked as failed. If the source drive fails, both the source drive and the hot spare drive are marked as failed.

> A cold swap requires that you power down the system before replacing a defective drive in a disk subsystem.

> Rebuilding

> If a drive fails in a drive group that is configured as a RAID 1, RAID 5, or RAID 10 virtual drive, you can recover the lost data by rebuilding the drive. If you have configured hot spares, the Nytro controller card automatically tries to use them to rebuild failed drives. Manual rebuild is necessary if hot spares with enough capacity to rebuild the failed drives are not available. You must insert a drive with enough storage into the subsystem before rebuilding the failed drive.

DB15-001059-00-April 2013
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