On 04/24/2012 12:53 PM, Bernhard Voelker wrote: > > > On 04/24/2012 01:15 PM, Pádraig Brady wrote: >>> With those changes, the affected files are then very compressible. >>>> With some file system types/options, won't they occupy far fewer >>>> blocks than before? >> Good point. >> The dd/sparse one could then fail the alloc check. >> The fiemap-empty change is only 5120 bytes too. > > Wouldn't > > -dd count=10 if=/dev/urandom conv=notrunc iflag=fullblock > of=unwritten.withdata > +dd count=10 if=/dev/zero | sed 's/\(.\)./\1 /g' | dd conv=notrunc > of=unwritten.withdata > > defeat the compression logic?
You'd have to be approaching random to avoid compression. $ dd count=10 if=/dev/zero | tr '\0' 1 | gzip -c | wc -c 41 $ dd count=10 if=/dev/zero | sed 's/\(.\)./\1 /g' | gzip -c | wc -c 41 cheers, Pádraig.
