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-rw-r--r--examples/guestfs-faq.pod19
1 files changed, 19 insertions, 0 deletions
diff --git a/examples/guestfs-faq.pod b/examples/guestfs-faq.pod
index 7ca534ab..28257437 100644
--- a/examples/guestfs-faq.pod
+++ b/examples/guestfs-faq.pod
@@ -405,6 +405,25 @@ C<$TMPDIR/.guestfs-E<lt>UIDE<gt>> is used instead.
It is safe to delete this directory when you are not using libguestfs.
+=head2 virt-sparsify seems to make the image grow to the
+full size of the virtual disk
+
+If the input to L<virt-sparsify(1)> is raw, then the output will be
+raw sparse. Make sure you are measuring the output with a tool which
+understands sparseness such as C<du-sh>. It can make a huge difference:
+
+ $ ls -lh test1.img
+ -rw-rw-r--. 1 rjones rjones 100M Aug 8 08:08 test1.img
+ $ du -sh test1.img
+ 3.6M test1.img
+
+(Compare the apparent size B<100M> vs the actual size B<3.6M>)
+
+If all this confuses you, use a non-sparse output by specifying the
+I<--convert> option, eg:
+
+ virt-sparsify --convert qcow2 disk.raw disk.qcow2
+
=head1 USING LIBGUESTFS IN YOUR OWN PROGRAMS
=head2 The API has hundreds of methods, where do I start?