A reduced resolution dataset (.rrd) file is one method of storing the pyramid layers for a raster dataset. An .rrd file is created in possible two scenarios:
- The file format is an ERDAS IMAGINE (.img) file.
- The pyramids are built with a version prior to ArcGIS 10.
RRD file requirements
A requirement for building an .rrd file for a raster dataset is to have write access to the directory where the dataset resides. The .rrd file will be created in the same directory as the source dataset when you choose to build pyramids. The next time you add this raster dataset, these pyramids will be used. One exception to this rule is ERDAS IMAGINE files, where the pointer to the pyramids is stored in the image file rather than an auxiliary (.aux) file like other formats. In this case, you must have write access to the raster dataset and the directory in which it resides.
RRD file size
For decompressed rasters, the minimum .rrd file size is approximately 8 percent of the size of the original raster dataset. In certain situations, however, the size of the .rrd file created can be larger (33%) than the original file, depending on the compression technique used in the original raster file. If your .rrd file exceeds two gigabytes, a reduced resolution dataset external (.rde) raster data file is created as a supplementary file.
Below is an example of the increase in the storage size of a raster dataset due to the use of full pyramid levels. Level 0 is the original raster dataset.
| Pyramid level | Percent increase of level 0 | Total size on disk |
|---|---|---|
0 | N/A | 1 GB |
1 | 25.0% | 1.25 GB |
2 | 6.25% | 1.313 GB |
3 | 1.56% | 1.328 GB |
4 | 0.4% | 1.332 GB |
5 | 0.1% | 1.333 GB |
6 | 0.024% | 1.3332 GB |
7 | 0.006% | 1.3333 GB |