r.buildvrt: document performance issues with external data (#4441)

* document performance issue * address code review * Apply suggestions from code review Co-authored-by: Markus Neteler <[email protected]> * consistent recommendation * remove leftover dot --------- Co-authored-by: Markus Neteler <[email protected]>
OSGeo · Oct 31, 2024 · f9f01e1 · f9f01e1
1 parent ba0a495
commit f9f01e1
Showing 1 changed file with 13 additions and 0 deletions.
diff --git a/raster/r.buildvrt/r.buildvrt.html b/raster/r.buildvrt/r.buildvrt.html
@@ -12,6 +12,8 @@ <h2>NOTES</h2>
 the original raster maps which is only valid if the original raster
 maps remain in the originally indicated mapset. A VRT can also be built
 from raster maps registered with <em><a href="r.external.html">r.external</a></em>.
+However, GRASS VRTs built from external registered data (see below)
+are known to have performance issues.
 
 <p>
 Reading the whole VRT is slower than reading the equivalent single
@@ -48,12 +50,23 @@ <h3>VRT from a DEM in the North Carolina sample dataset</h3>
 r.buildvrt file=tilelist.csv output=elev_state_50m_vrt
 </pre></div>
 
+<h2>KNOWN ISSUES</h2>
+
+Users may experience significant performance degradation with virtual rasters built
+with <em>r.buildvrt</em> over GDAL-linked (<em>r.external</em>) raster maps,
+especially on slower file systems with latency like NFS. Performance degradation
+may also occur on local file systems, but is usually less severe. For such use cases
+consider using the GRASS GIS addon
+<a href="https://grass.osgeo.org/grass-stable/manuals/addons/r.buildvrt.gdal.html">r.buildvrt.gdal</a>
+or building GDAL VRTs, e.g. with <em>gdalbuildvrt</em>.
+
 <h2>SEE ALSO</h2>
 
 <em>
 <a href="r.tile.html">r.tile</a>,
 <a href="r.patch.html">r.patch</a>,
 <a href="r.external.html">r.external</a>
+<a href="https://grass.osgeo.org/grass-stable/manuals/addons/r.buildvrt.gdal.html">r.buildvrt.gdal</a>
 </em>
 
 <p>