| PRIMECLUSTER Global Disk Services Configuration and Administration Guide 4.1 (Solaris(TM) Operating System) |
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| Appendix A General Notes | > A.2 Important Points |
Out of the physical disk area, the capacity available for creating volumes equals the physical disk size rounded down to the cylinder boundary, minus the private slice size. This size is called the available size of disk.
Private slice is an area that GDS reserves on each disk for storing data, such as configuration information and the JRM log.
When a physical disk is registered with a class, a private slice is reserved. Disks within the same class will all have the same private slice size. The size is determined by the size of the disk that is first registered with the class.
The size of a private slice can be estimated as below. The private slice size never exceeds the following estimated values.
When the size of the disk first registered with the class is 10GB and below:
32MB
When the size of the disk first registered with the class is over 10GB:
32MB + (0.1% of the disk capacity to the cylinder boundary, rounded-up)
The size of a log for JRM is determined by the size of the volume. As a result, the log area for JRM may not be reserved because the private slice size becomes insufficient when a mirror volume is created registering a disk larger in size than the first registered disk with the class. In such a case, the volume is incapable of using JRM. Therefore you are recommended to first register a disk of the maximum size with the class.
When physical disks are registered with shadow classes, the sizes of private slices are determined based on those saved in the VTOC of the physical disks. For this reason, regardless of the order of registering physical disks with shadow classes, the sizes of private slices of the shadow classes become consistent with those of the corresponding disk classes. In other words, the order of registering physical disks with shadow classes is not a cause for concern.
Cylinder Size
The cylinder size of a disk registered with a local class or a shared class is 32,768 blocks (= 16 MB). To calculate the sizes of disks to register with local classes or shared classes, assume that the cylinder size is 16 MB.
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