What is shelf loss protection and drawer loss protection?
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Shelf loss protection and drawer loss protection are attributes of pools and volume groups that allow you to maintain data access in the event of a single shelf or drawer failure.
Shelf loss protection
A shelf is the enclosure that contains either the drives or the drives and the controller. Shelf loss protection guarantees accessibility to the data on the volumes in a pool or volume group if a total loss of communication occurs with a single drive shelf. An example of total loss of communication might be loss of power to the drive shelf or failure of both I/O modules (IOMs).
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Shelf loss protection is not guaranteed if a drive has already failed in the pool or volume group. In this situation, losing access to a drive shelf and consequently another drive in the pool or volume group causes loss of data. |
The criteria for shelf loss protection depends on the protection method, as described in the following table.
| Level | Criteria for shelf loss protection | Minimum number of shelves required |
|---|---|---|
Pool |
The pool must include drives from at least five shelves and there must be an equal number of drives in each shelf. Shelf loss protection is not applicable to high-capacity shelves; if your system contains high-capacity shelves, refer to Drawer Loss Protection. |
5 |
RAID 6 |
The volume group contains no more than two drives in a single drawer. |
3 |
RAID 3 or RAID 5 |
Each drive in the volume group is located in a separate shelf. |
3 |
RAID 1 |
Each drive in a RAID 1 pair must be located in a separate shelf. |
2 |
RAID 0 |
Cannot achieve Shelf Loss Protection. |
Not applicable |
Drawer loss protection
A drawer is one of the compartments of a shelf that you pull out to access the drives. Only the high-capacity shelves have drawers. Drawer loss protection guarantees accessibility to the data on the volumes in a pool or volume group if a total loss of communication occurs with a single drawer. An example of total loss of communication might be loss of power to the drawer or failure of an internal component within the drawer.
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Drawer loss protection is not guaranteed if a drive has already failed in the pool or volume group. In this situation, losing access to a drawer (and consequently another drive in the pool or volume group) causes loss of data. |
The criteria for drawer loss protection depends on the protection method, as described in the following table:
| Level | Criteria for drawer loss protection | Minimum number of drawers required |
|---|---|---|
Pool |
Pool candidates must include drives from all drawers, and there must be an equal number of drives in each drawer. |
5 |
RAID 6 |
The volume group contains no more than two drives in a single drawer. |
3 |
RAID 3 or 5 |
Each drive in the volume group is located in a separate drawer |
3 |
RAID 1 |
Each drive in a mirrored pair must be located in a separate drawer. |
2 |
RAID 0 |
Cannot achieve Drawer Loss Protection. |
Not applicable |