380Administering hot-relocation

How hot-relocation works

How hot-relocation works

Hot-relocation allows a system to react automatically to I/O failures on redundant (mirrored or RAID-5) VxVM objects, and to restore redundancy and access to those objects. VxVM detects I/O failures on objects and relocates the affected subdisks to disks designated as spare disks or to free space within the disk group. VxVM then reconstructs the objects that existed before the failure and makes them redundant and accessible again.

When a partial disk failure occurs (that is, a failure affecting only some subdisks on a disk), redundant data on the failed portion of the disk is relocated. Existing volumes on the unaffected portions of the disk remain accessible.

Note: Hot-relocation is only performed for redundant (mirrored or RAID-5) subdisks on a failed disk. Non-redundant subdisks on a failed disk are not relocated, but the system administrator is notified of their failure.

Hot-relocation is enabled by default and takes effect without the intervention of the system administrator when a failure occurs.

The hot-relocation daemon, vxrelocd, detects and reacts to VxVM events that signify the following types of failures:

Disk failure

This is normally detected as a result of an I/O failure from a

 

VxVM object. VxVM attempts to correct the error. If the

 

error cannot be corrected, VxVM tries to access

 

configuration information in the private region of the disk.

 

If it cannot access the private region, it considers the disk

 

failed.

Plex failure

This is normally detected as a result of an uncorrectable I/O

 

error in the plex (which affects subdisks within the plex).

 

For mirrored volumes, the plex is detached.

RAID-5 subdisk failure

This is normally detected as a result of an uncorrectable I/O

 

error. The subdisk is detached.

When vxrelocd detects such a failure, it performs the following steps:

■vxrelocd informs the system administrator (and other nominated users) by electronic mail of the failure and which VxVM objects are affected.

See “Partial disk failure mail messages” on page 383. See “Complete disk failure mail messages” on page 384. See “Modifying the behavior of hot-relocation” on page 395.

■vxrelocd next determines if any subdisks can be relocated. vxrelocd looks for suitable space on disks that have been reserved as hot-relocation