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.
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:
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.
vxrelocd detects such a failure, it performs the following steps:
vxrelocdinforms the system administrator (and other nominated users) by electronic mail of the failure and which VxVM objects are affected.
vxrelocdnext determines if any subdisks can be relocated.
vxrelocdlooks for suitable space on disks that have been reserved as hot-relocation spares (marked
spare) in the disk group where the failure occurred. It then relocates the subdisks to use this space.
vxrelocduses free space on disks in the same disk group, except those disks that have been excluded for hot-relocation use (marked
vxrelocdhas relocated the subdisks, it reattaches each relocated subdisk to its plex.
vxrelocdinitiates appropriate recovery procedures. For example, recovery includes mirror resynchronization for mirrored volumes or data recovery for RAID-5 volumes. It also notifies the system administrator of the hot-relocation and recovery actions that have been taken.
If relocation is not possible,
vxrelocd notifies the system administrator and takes no further action.
Relocation of failing subdisks is not possible in the following cases:
vxrelocd(1M) manual page.
Example of hot-relocation for a subdisk in a RAID-5 volume shows the hot-relocation process in the case of the failure of a single subdisk of a RAID-5 volume.
Example of hot-relocation for a subdisk in a RAID-5 volume
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