VDS with LOD levels unexpectedly large
I find VDS data sets to increase much more in size when LOD levels are added than expected.
Obervation/Experiment
I created a VDS data sets from a volve data set (ST0202R08_PS_PSDM_FULL_OFFSET_PP_TIME.MIG_FIN.POST_STACK.3D.JS-017534.segy
, about 1GiB) for different LOD levels. This is a 3D post-stack dataset such that I would expect an increase in file size of about 15% if all LOD levels are created. The major increase should appear for the first few LOD levels.
I observe the following file sizes:
LOD level | Size in MiB | Relative size |
---|---|---|
0 | 864,04 | 100% |
1 | 1248,06 | 144% |
2 | 1456,09 | 169% |
3 | 1456,09 | 169% |
4 | 1454,31 | 168% |
5 | 1456,09 | 169% |
6 | 1456,09 | 169% |
7 | 1456,09 | 169% |
8 | 1456,09 | 169% |
9 | 1454,88 | 168% |
10 | 1456,10 | 169% |
11 | 1456,10 | 169% |
12 | 1456,11 | 169% |
Now I see that the file size increases by more than 50%. If I scale my estimate I see that the increase at least flattens out quickly what agrees with the geometric series. However, I also see a small dip for LOD level 10 and 11 which I don't exactly understand, but maye that is due to some collapsed blocks.
I used the default settings, but also tested with LOD level and compression set explicitly with the same results for the file size. The file is stored on a local hard drive and file size is checked with du
.
I also tested with a larger SEGY where VDS with no LOD levels is 11 GiB large. When adding 4 LOD levels the file size goes up to 20 GiB. This is an increase of file size by even more than 80%.
Questions
Is this increase in file size expected? I assumed that the file size increase should be according to the geometric series with a=1
and r=(1/2)^d
which would be r=1/8
for 3D data sets.
Platform
- Apple Arm M1 Max
- MacOS 13.2.1
- OpenVDS 3.0.3 (compiled from source)