Available size of a disk
Within 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.
Size of a private slice
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. If using a shared class or a local class, the private slice size of the class is decided depending on the disk size first registered in the class.
The size of a private slice can be estimated as below. The estimated value below is the maximum size reserved for the private slice on the physical disk. The private slice size never exceeds the estimated values.
Root class
11 MB
Shared disk or local class
When the size of the disk first registered with the class is 10 GB and below:
32 MB
When the size of the disk first registered with the class is over 10 GB:
32 MB + (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 of the private slices stored in the disk label 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.
1 TB or larger disks
If a 1 TB or larger disk is registered with a class and managed, the disk label must be EFI type. If the disk label type is VTOC or no disk label has been created, use the format(1M) command to create an EFI label before registering it with a class. For details of disk label types, see "A.2.5 Disk Label."
Registration/deletion of high-capacity EFI label disk
When using high-capacity EFI label disk, registration and deletion of disk may take time. Execution time varies depending on the system, but the following will serve as a guide: (Calculating using both procedures will have the same value. Use the easier calculation.)
1 minute for each 1 GB size of a private slice
1 minute for each 1 TB size of disk first registered to the class
