Product manual

CDA 7 5630 Product Manual
2-8 77 A1 69UP Rev00
2.3.1 FBA Data and Command Format
FBA disk devices store data in fixed sized blocks (typically 512 bytes). A disk
device using FBA format is viewed as a large array of blocks. The physical
position of the block (cylinder and track) is usually not significant to the host.
When requesting disk access for read or write, the host addresses the device by the
logical block address (LBA) of the starting block and a count of the total blocks
needed. CDA 7 SCSI channel directors and disk directors control access to cache
and disk devices, responding to host requests as a standard SCSI disk device.
2.3.2 Logical Volume Structure for GCOS 7 environment
The channel directors interact with cache. Therefore, there is no mechanical
meaning to cylinders, tracks, and heads on the CDA 7 logical volume from the
front end point of view.
However, CDA 7 uses a logical geometry definition for its logical volume
structure. This geometry is reflected in the SCSI mode sense data available to the
host.
CDA 7 uses the following logical volume structure:
• Each logical volume has N cylinders
• Each cylinder has 15 tracks (heads)
• Each track has 64 blocks of 512 bytes
Therefore, a CDA 7 logical volume with N cylinders has a usable block capacity
of:
N * 15 * 64
“N” for each volume is defined during CDA 7 configuration.
Table 2-1. Cylinders per Logical Volume/or Split Physical Devices
Physical Disk Device Size 2 Logical Volumes per Disk Device
Unformatted capacity of 23 GB
Formatted capacity 18 GB (3.5")
18,414 Cylinders x 2
8.42 GB2 x 2 (9.05 GB10 x 2)
To calculate the size of the logical volume:
# of Cylinders * Heads * Blocks * 512
(N * 15 * 64 * 512)