Hi,
I am experiencing significant performance issues with virtual rasters build with r.buildvrt over GDAL-linked (r.external) raster maps (source is in GeoTiff format) on NFS.
The GeoTiff data are located on a relatively fast NFS network storage, while the GRASS DB is located on a somewhat slower NFS storage system.
In order to drill down to the issue I ran r.univar on three GDAL linked raster maps that cover my computational region. The process which consists of three r.univar runs takes ~40 seconds.
Using the same computational region, one r.univar on a virtual raster of the same three raster map has not finished after 30 minutes. After converting the GDAL linked maps to native GRASS format (on the slower NFS) I built a VRT over the GRASS GIS format raster maps. For that VRT, performance is almost identical to to r.univar onr the individual raster maps (= no VRT). So it seems the issue is reading GDAL linked raster maps through GRASS VRTs.
Is that a limitation of virtual rasters in GRASS GIS or is it a bug in how VRTs are read? Is there a point to open an issue for this?
Currently, VRT with GDAL linked data seems practically unusable... Any suggestions on what can be done is very welcome. Would be a pity if I had to abandon VRTs...
Cheers,
Stefan
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