Allocation Map and Statistics Overhead
The TVS layer requires space on each pdisk for its allocation map, device tag, and statistics areas. The number of cylinders required depends on the pdisk size as specified in the vconfig GDO. The following table lists the overhead for disk sizes ranging from 60 GB through 1,024 GB, using a value for 1 GB as 1024 * 1024 * 1024 bytes.
Be aware that the size of this file can change from release to release.
You can use the following equation to determine the number of cylinders required:
where:
|
Equation Element … |
Represents the … |
|
E |
number of cylinders on the device, which is determined as follows:  where N represents the number of 512‑byte sectors in the partition on the pdisk, as indicated by the PDISK entry in the vconfig.txt file. Devices with a sector size of 4096 bytes are also expressed in units of 512 bytes for the purposes of this equation (so, for example, a device with 1000 4096-byte sectors would have N=8000). |
|
A |
number of TVS vprocs that share the device. |
|
roundup |
function used to round up the number of cylinders. The function is defined as follows:  |
|
m |
TVS map block size: |
|
d |
Map entries per map block: |
|
t |
TVS device tag size (in units of 512): |
|
p |
Alignment:
|
The following table shows a few sample results for various disk sizes:
|
Disk Size (GB) |
Allocation Map and Statistics Space Required (cylinders) |
|
60 |
1 |
|
203 |
4 |
|
474 |
8 |
|
744 |
12 |
|
1,014 |
16 |
Space is also required on system disk in the tpi-data directory for the allocator memory‑mapped file. Note that tpi‑data is stored on system disk in a node, not on the user data space on the disk array. The amount of space required depends on the size and number of pdisks and how many allocators there are. For most system configurations, the size of this file ranges between 5 and 40 MB.