-The filesystem options C<sync> and C<noatime> are set with this
-call, in order to improve reliability.");
+B<Important note:>
+When you use this call, the filesystem options C<sync> and C<noatime>
+are set implicitly. This was originally done because we thought it
+would improve reliability, but it turns out that I<-o sync> has a
+very large negative performance impact and negligible effect on
+reliability. Therefore we recommend that you avoid using
+C<guestfs_mount> in any code that needs performance, and instead
+use C<guestfs_mount_options> (use an empty string for the first
+parameter if you don't want any options).");