Andrew,

> When I create a mask band in a large lzw-compressed or jpeg-compressed tif
> using the COG driver it dramatically increases processing time over writing
> RGBA (hours instead of minutes), so the issue is not jpeg compression, it's
> the creation of the mask band. Steps to reproduce:

There's clearly some complications & overhead internally to be able to deal 
with non-alpha 
mask bands. I wouldn't have expected it to be as large as you observed though. 
Would 
require deeper investigation to understand why that causes such performance 
difference.

By the way, you can drop ---config GDAL_TIFF_INTERNAL_MASK YES when using the 
COG 
driver. It sets it automacally.

> I also noticed that the -co BIGTIFF=NO option appears to be ignored in the
> COG driver. I can share a file if that's helpful (can not provide a link on
> the listserv)

I can't reproduce that:

gdal_translate byte.tif out.tif -of cog -co bigtiff=yes : creates a bigtiff file

gdal_translate byte.tif out.tif -of cog -co bigtiff=no -outsize 80000 80000 -co 
overviews=none
fails with "The TIFF file will be larger than 4GB, so BigTIFF is necessary.  
Creation failed."

Even

-- 
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