In addition to the space it consumes in a VOB database, each element
requires space in the VOB’s source pool and usually other pools.
Every version of every element in the VOB is stored in a container
file in a source pool. Different element types have different type managers.
Most type managers compress source data so that each version consumes less
storage in the source pool than it does in cleartext form.
Table 1 lists
compression ratios for commonly used built-in type managers.
Table 1. Type manager compression ratios| Type manager |
Type description |
Compression ratio |
|---|
| whole_copy |
Whole copy of object |
1:1 |
| text_file_delta |
Interleaved deltas of printable text |
50:1 |
| z_whole_copy |
Compressed whole-copy |
2.5:1 |
| z_text_file_delta |
Compressed text_file_delta |
200:1 |
With the information provided in Table 1,
you could compute a rough approximation of VOB source pool size by using this
formula:
P = N * V * S / C
where:
- P is the source pool size in bytes.
- N is the number of elements in the VOB.
- V is the average number of versions per element
- S is the average file size of each cleartext element
version.
- XSC is the compression ratio of the element’s type
manager.
The following example uses this formula to estimate the size of
the source pool of a VOB that contains 500 elements of type text_file_delta,
with an average of 20 versions per element and an average version size of
50000 bytes:
500 * 20 * 50000 / 50 = 10,000,000 bytes
For VOBs
that contain elements of different types, you must repeat this calculation
for each element type.
Elements also require space in the cleartext
and DO pools, which are caches that are periodically scrubbed to control their
growth. Because space requirements of cleartext and DO pools are determined
by site-specific patterns of use, there is no general rule for estimating
their size based on the number of elements in a VOB.
For more information
about VOB storage pools, see VOB storage pools.