UDF File Sysyem Fundamentals
Data files are written on a CD by fitting the data into the recording blocks. This is done in one of two fundamentally different ways: the ISO file system, or the UDF file system.
The ISO File System
ISO allows the ‘Joliet’ extensions to support Windows-style long file names. In this method, all the files to be written are selected and then written to the disk with a Table of Contents (TOC). Together, these files and TOC form a session. If the disk has not been filled, it can be put back into the writer, and a further session written.
In this method of writing, the files cannot be individually changed or deleted. If on a CD-RW disk, they can only be erased as a whole. The ISO file system is mostly used, therefore, with CD-R media.
The UDF File System
This method the disk is first formatted into packets which then behave very much like the sectors of a hard disk. These of packets are written as an individual operation. Those files can be selectively erased or updated. Therefore, such a CD is described as behaving as a “giant floppy”. UDF allows files to be dragged and dropped to and from the CD in Windows Explorer, just as to and from a hard disk.
Reading such disks needs special software in earlier versions of Windows, and may not be possible with all CD drives, even when that software is present.
READING UDF FORMAT DISKS IN WINDOWS XP
XP’s Windows Explorer does have some support for UDF disks, which will allow you to read those produced by some third party software. Please note that this is strictly a read-only matter. There is no way to write to an UDF disk in XP: you cannot add files to one, nor can you delete individual files from an existing disk, nor update any single file. All you can do is erase the entire disk.
Why UDF?
Any removable media (CD, DVD, flash drive, external hard drive, etc) needs a file system format. Ideally, this format should have these characteristics:
- Can be understood by different platforms. This makes it possible to copy files between Windows, Mac, and Unix systems.
- Its specification is open. ISO9660 is an open standard, while FAT belongs to Microsoft.
- Has rich features (preferably a super set of all common file systems) so information won't be lost when files are copied to this file system.
- Can support different kinds of physical media. Optical media is very different from hard drives. Some media is write once (CD-R, DVD-R, DVD+R, BD-R), some needs defect-management (CD-RW, DVD-RW, DVD+RW, BD-RE, etc), some needs to be expanded sequentially before being overwritten (most RW media).
UDF is the only file system that meets all these standards, since it was designed for the information exchange purpose.
- Large partition size (maximum 2TB with 512B block size, or 8TB with 2KB block size)
- 64-bit file size
- Extended attributes (e.g., named streams, or forks) without size limitation
- Long file names (maximum 254 bytes, any character can appear in the name)
- Unicode encoding of file names
- Sparse file
- Hard links
- Symbolic links
- Metadata checksum
- Metadata redundancy (optional in UDF 2.50 or later in metadata partition)
- Defect management (for media that does not manage defect internally, such as CD-RW, DVD-RW, and DVD+RW)
- UDF defines how different platforms interact with each other. For example, it defines how to store Mac Finder Info and Resource Fork, NTFS ACL, UNIX ACL, OS/2 EA, etc. It also requires platforms to preserve the information that they don't understand.
- UDF is a truly universal file system. It can be used on all kinds of optical media, including read only (CD-ROM, DVD-ROM, BD-ROM (Blu-ray Disc Read-Only)), write once (CD-R, DVD-R, DVD+R, BD-R), rewritable (CD-RW, DVD-RW, DVD+RW, DVD-RAM, CD-MRW, DVD+MRW, BD-RE), and of course block device (hard drives). Even write-once media appears as a big overwritable floppy under UDF.
How to burn with UDF?
Most third-party programs will allow you to create a DVD-Rom or CD-Rom with the UDF file format. In this example I will be using NERO burning ROM to create a DVD-Rom.
1) Open Program and choose the disk type and format.
A) Choose disk type
B) Choose format
C) Click new
2) Choose Files to Write / Burn on to disk.
A) Use File Browser to navigate
B) Click and drag files on CD / DVD Image ( Area B2 )
C) Click Burn Button
3) Burn Compilation
Nero will open a small window that will allow you to select and check all disk burning options one more time before completing the disk. For most purposes the standard settings will suffice.
Click Burn one more time
4) The last step
Nero will ask for an empty disk to write to. The DVD-R tray will open automatically. Make sure that you have to correct type of disk. Insert the disk and close the tray. The program will automatically burn to compilation.
