Logical slices are the smallest objects managed by GDS. A logical slice is also simply referred to as "slice."
Mirror volume is created by mirroring more than one logical slice. Each mirror volume will have one logical slice for every disk and lower level group belonging to the mirror group.
A single volume, stripe volume and a volume in concatenation group will each consist of one logical slice.
A switch volume consists of one logical slice, which is on the active disk.
Usually, an application cannot access the slices consisting a volume. But in the case of a mirror volume with its physical slice attribute set to "on," temporarily detaching the slice will allow the application to directly access the slice. A snapshot (replication) of the volume can be created with this function.
Attributes
A slice has the following attributes.
This attribute identifies the slice within a class.
This attribute indicates the just resynchronization mechanism mode for slices.
JRM for slices is enabled.
JRM for slices is disabled.
This attribute sets the access mode. The value can be set to one of the following.
Sets access mode for read and write.
Sets access mode for read only.
Operation
The following operations are available for slices.
A snapshot of a mirror volume can be created by detaching one of the slices consisting the mirror volume with the sdxslice -M command.
For details on GDS Management View, see "5.3.2.1 Backup (by Slice Detachment)."
The temporarily detached slice can be attached to the volume again with the sdxslice -R command.
For details on GDS Management View, see "5.3.2.1 Backup (by Slice Detachment)."
The detached slice can be activated with the sdxslice -N command.
For details on GDS Management View, see "5.3.2.1 Backup (by Slice Detachment)."
The detached slice can be stopped with the sdxslice -F command.
For details on GDS Management View, see "5.3.2.1 Backup (by Slice Detachment)."
Detached slice can be taken over from another node with the sdxslice -T command.
The operation from GDS Management View is unsupported.
Slice status can be displayed with the sdxinfo command.
For details on GDS Management View, see "5.3.1 Viewing Configurations/Statuses and Monitoring Statuses."
Attribute values of the detached slice can be changed with the sdxattr -S command.
The operation from GDS Management View is unsupported.
Status
A slice can have the following status.
Data is normal, and accessible.
Here, the volume is ACTIVE. The total number of slices that are in the ACTIVE, STOP, or COPY status (in process of background copying) within the mirror volume indicates the present multiplicity of the mirroring configuration (1 to 8).
Data is normal, but inaccessible.
Here, the volume is in the STOP status. The total number of slices that are in the STOP, ACTIVE, or COPY (in process of background copying) status within the mirror volume indicates the present multiplicity of the mirroring configuration (1 to 8).
Data is invalid and inaccessible.
When an I/O error is detected in a slice during the mirroring process, the slice becomes INVALID. Promptly identify the problem and restore the slice based on the disk driver message or the like. After restoring the slice, execute the synchronization copying. When it ends successfully, the slice will be valid (the slice will be made the ACTIVE or STOP status). If it fails, it will be INVALID again.
Synchronization copying is in process to ensure the data integrity.
Synchronization copying is executed from a slice in the valid status (ACTIVE or STOP) to a slice in the COPY status. When it ends successfully, the slice will be made valid (ACTIVE or STOP). If it fails, it will be INVALID.
The slice is temporarily detached from the volume and can be accessed independently.
When the sdxslice -M command ends successfully, the slice is made the TEMP status. To restore the status (ACTIVE or STOP), execute the sdxslice -R command.
The slice is temporarily detached from the mirror volume, but cannot be accessed separately.
To make the slice accessible, activate the slice executing the sdxslice -N command or the sdxslice -T command.
The slice is inaccessible for a special reason.
When the disk is not available for operation (DISABLE or SWAP), all slices related to the disk are made the NOUSE status.
Reference
There are the following points of concern for slices.
Figure 2.7 Logical Slice
