wrong of me, it uses iso9660, here is the link where you can read more.
http://fy.chalmers.se/~appro/linux/DVD+RW/
Formatting the DVD+RW media. Virgin DVD+RW media needs to be initally formatted prior usage. Once again, only virgin DVD+RW media needs to be formatted. As of version 5.10 growisofs detects blanks and applies initial formatting procedure automatically. Otherwise same effect can be achieved by passing the device name, e.g. /dev/scd0, as an argument to dvd+rw-format. To make formatting process reasonably fast, less than 1 minute, the media gets formatted only partially, as you can notice by observing a progress indicator displayed by dvd+rw-format. The final indicator value varies from firmware to firmware, values as low as 1.6% were observed. But it does not mean that you can only write that little. The unit keeps formatting transparently, as you add more data. Oh! Do keep in mind that DVD capacity of 4.7GB are salesman's GB, i.e. 10003 and not 10243.

It was observed that excessive reformats can render media unusable already after 10-20 reformats. It appears to be a firmware deficiency, not some common media defect [at least it was perfectly possible to salvage the media in a unit of different brand], but I don't recommend [enforced] reformat in either case. Note that DVD+RW re-formatting procedure does not substitute for blanking. If you want to nullify the media, e.g. for privacy reasons, do it explicitly with 'growisofs -Z /dev/scdN=/dev/zero'. Otherwise just write over previous recording as it simply wasn't there, no re-formatting is required.

DVD+R media does not require any formatting procedure applied and is ready to use out-of-the-box. Apparently, a reminder that 1st generation units (Ricoh MP5120A and derivatives) are not capable of burning DVD+R is needed.