Hot Spares A hot spare is an extra, unused drive that is part of the disk subsystem. It is usually in Standby mode, ready for service if a drive fails. Hot spares permit you to replace failed drives without system shutdown or user intervention. Nytro MegaRAID SAS RAID cards can implement automatic and transparent rebuilds of failed drives that use hot spare drives, which provides a high degree of fault tolerance and zero downtime. The RAID management software allows you to specify drives as hot spares. When a hot spare is needed, the RAID controller assigns the hot spare that has a capacity closest to and at least as great as that of the failed drive to take the place of the failed drive. The failed drive is removed from the virtual drive and is marked ready awaiting removal after the rebuild to a hot spare starts. You can make hot spares of the drives that are not in a RAID virtual drive. You can use the RAID management software to designate the hot spare to have enclosure affinity, meaning that if drive failures are present on a split backplane configuration, the hot spare is used first on the backplane side in which it resides. If the hot spare is designated as having enclosure affinity, it attempts to rebuild any failed drives on the backplane in which it resides before rebuilding any other drives on other backplanes. 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. The following subsections describe the two hot spare types: Global Hot Spare Use a global hot spare drive to replace any failed drive in a redundant drive group if its capacity is equal to or larger than the coerced capacity of the failed drive. A global hot spare defined on any channel must be available to replace a failed drive on both channels. Dedicated Hot Spare Use a dedicated hot spare to replace a failed drive only in a selected drive group. One or more drives can be designated as a member of a spare drive pool. The most suitable drive from the pool is selected for failover. A dedicated hot spare is used before one from the global hot spare pool. Hot spare drives can be located on any RAID channel. Standby hot spares (not being used in a RAID drive group) are polled every 60 seconds at a minimum, and their status made available in the drive group management software. Nytro MegaRAID controllers can rebuild with a disk that is in a system but not initially set to be a hot spare. Observe the following parameters when using hot spares: Hot spares are used only in drive groups with redundancy: RAID levels 1, 5, 6, 10, 50, and 60. A hot spare connected to a specific controller can rebuild a drive that is connected only to the same controller. You must assign the hot spare to one or more drives through the controller BIOS or use drive group management software to place it in the hot spare pool. A hot spare must have free space equal to or greater than the drive it replaces. For example, to replace an 500-GB drive, the hot spare must be 500 GB or larger.
Hot Spares
A hot spare is an extra, unused drive that is part of the disk subsystem. It is usually in Standby mode, ready for service if a drive fails. Hot spares permit you to replace failed drives without system shutdown or user intervention. Nytro MegaRAID SAS RAID cards can implement automatic and transparent rebuilds of failed drives that use hot spare drives, which provides a high degree of fault tolerance and zero downtime.
The RAID management software allows you to specify drives as hot spares. When a hot spare is needed, the RAID controller assigns the hot spare that has a capacity closest to and at least as great as that of the failed drive to take the place of the failed drive. The failed drive is removed from the virtual drive and is marked ready awaiting removal after the rebuild to a hot spare starts. You can make hot spares of the drives that are not in a RAID virtual drive.
You can use the RAID management software to designate the hot spare to have enclosure affinity, meaning that if drive failures are present on a split backplane configuration, the hot spare is used first on the backplane side in which it resides.
If the hot spare is designated as having enclosure affinity, it attempts to rebuild any failed drives on the backplane in which it resides before rebuilding any other drives on other backplanes.
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.
The following subsections describe the two hot spare types:
Global Hot Spare
Use a global hot spare drive to replace any failed drive in a redundant drive group if its capacity is equal to or larger than the coerced capacity of the failed drive. A global hot spare defined on any channel must be available to replace a failed drive on both channels.
Dedicated Hot Spare
Use a dedicated hot spare to replace a failed drive only in a selected drive group. One or more drives can be designated as a member of a spare drive pool. The most suitable drive from the pool is selected for failover. A dedicated hot spare is used before one from the global hot spare pool.
Hot spare drives can be located on any RAID channel. Standby hot spares (not being used in a RAID drive group) are polled every 60 seconds at a minimum, and their status made available in the drive group management software. Nytro MegaRAID controllers can rebuild with a disk that is in a system but not initially set to be a hot spare.
Observe the following parameters when using hot spares:
Hot spares are used only in drive groups with redundancy: RAID levels 1, 5, 6, 10, 50, and 60.
A hot spare connected to a specific controller can rebuild a drive that is connected only to the same controller.
You must assign the hot spare to one or more drives through the controller BIOS or use drive group management software to place it in the hot spare pool.
A hot spare must have free space equal to or greater than the drive it replaces. For example, to replace an 500-GB drive, the hot spare must be 500 GB or larger.