In theory it shouldn't be too big a file, as all arithmetics are performed internally using 64-bit integers which support archives up to a few petabytes big. On the other hand, I've never tried eXtract against a 6Gb file. The best approach (for several reasons) is to use archive splitting to create 2Gb parts, then download and try to extract those backup parts using Akeeba eXtract Wizard or Kickstart.
Nicholas K. Dionysopoulos
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