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Universal Disc Format (UDF) -- WAS: HD Backup

On Mon, 2006-01-02 at 02:47 -0600, Stan Zaske wrote:
> This UDF cross platform file system for removeable hardrives has me curious. 
> How would one go about formating a drive with it. I'm a Linux "noob" and am 
> unable to share with my other PC's formatted with NTFS. I'm running Kubuntu 
> 5.10 AMD64 "Breezy Badger" by the way. @:D>

UDF is probably the most flexible filesystem you'll ever see.  Like a
block filesystem (Ext2/3, NTFS, etc...), it has structures, extents and
can be written to read/write.  Like a pre-mastered/archive** filesystem
(ISO9660, ustar/stream, etc...), it can be generated into a single file
that is only as large as its data.

- Pre-mastered/Archive UDF (most commonly known)

[ **NOTE:  The "dump" programs for various filesystems actually give it
similar capability, although with some limitations and not quite as
absolutely encapsulating -- e.g., xfsdump, e2fsdump, etc... ]

There are various user-space programs to use UDF as a pre-
mastered/archive filesystem.  E.g., mkisofs can generate UDF images,
instead of ISO9660.  This, of course, generates a pre-mastered/archived
"read-only" version that is not directly usable -- just like
ustar/stream** or dump is not.  So this is _not_, of course, what you
use for a removable/external drive.

[ **NOTE:  ustar/stream can be appended to, of course.  Then again, you
can have multitrack/multisession ISO/UDF media, etc... ]

- Block Filesystem UDF (reweritables, flash, removables, fixed)

As flash devices have started to pass the 8GiB (8.4GB) size, many are
now offering UDF as a filesystem option instead of FAT32 because of
various XP limitations beyond 32GiB (33.8GB) and 128GiB (137GB).  Newer
Rigid Removable Disc (RRD) drives, such as the IOMega Rev, also use UDF.
HD-DVD continues to standardize on UDF, and many BluRay supporters are
demanding UDF be the default format (even though BluRay has its own
filesystem -- long, long story). 

Like most "regular" filesystems, UDF has a kernel driver and a set of
userspace tools.  But that's where some of the similarities differ.  UDF
is clearly not a "high performance" filesystem**, being that it does all
sorts of checks and, being designed for removables -- especially optical
(where the write error rate is 10^9 versus the typical 10^13 for
magnetic) -- expedites commits.  This is also why it is being preferred
over FAT32 for newer flash/removables.  With DVD-RAM, it has an
integrated verify-after write (which cuts performance down 45%, but
reduces error rates 4-5 orders of magnitude).

[ **NOTE:  It's still a _lot_ faster than the user-space rewritable NTFS
drivers for Linux, in addition to being a lot safer. ]

Linux had UDF support very early on because Linux was used, like most
UNIX, was a key optical archiving platform.  From proprietary optical to
Panasonic PD-CD to the DVD-RAM standard and on-ward, UDF was around in
kernel 2.0 and various user-space tools sprung up around it.  Remember,
this was back when hard drive sizes were barely reaching 1GB, and
optical archiving jukeboxes were 10s of GBs, and a universal filesystem
was needed.

- Kernel driver:  udf

First off, see if your kernel has UDF built:  
  modinfo udf

Most kernel 2.6 versions should, and most latter 2.4 kernels should as
well.  Again, UDF support has been around since the 2.0 days, although
it wasn't really until the 2.3 experimental branch that it was largely
feature complete (version 0.9.x, circa 2000).

With the UDF driver, you can both read _and_ write to various UDF media
in addition to fixed disks -- various removable discs, CD-RW, DVD-RAM,
DVD-RW and DVD+RW.  Some removables need to be formatted UDF (DVD-RW,
DVD+RW), while others are hard-formatted UDF (DVD-RAM, many non-standard
removables).  E.g., you'll know a DVD-RAM disc when you see it, it's got
"dash holes" in it which is its hard-formatted UDF CLV (constant linear
velocity -- CAV, CLV and CLV-Z are not a big deal for "single groove
recorded" media, but make all the difference in "a pie-slice/like-a-
fixed disc" rewritables ;-).

The issue is when you need to format UDF on a media that doesn't come
preformatted.  This would, of course, included fixed disks or those with
disk labels and slices (partition table and partitions).

- User-space tools:  udftools

The UDF tools were a compilation of various UDF tools that were separate
in the '90s (and were a pain to track down individually).  The 0.9.x
release (which matched the kernel driver) has been stable since the
2000.  There have been a few augmentations and improvements, resulting
in the 1.0.0 beta releases since early 2002.  The latest was the 1.0.0b3
release in early 2004 -- which seems to be largely a release that
addresses kernel 2.5/2.6 and DVD+RW.

The UDF SourceForge page for the UDF tools is here:  

The user-space tools included are as follows ...

  cdrwtool -- allows you to blank CD-RW (and some other, depending on
kernel support) media.  You won't need this tool for hd slices
(partitions), and you should only use it when directed for your exact
DVD drive type** and media.

  mkudffs -- make UDF filesystem.  About the only options to be aware of
are "--media-type" (you'll want to use "hd") and the character set
options ("--u8" "--u16" and "utf8" -- you'll want "--u16" for Windows
compatibility IIRC, but it should be the default).  Windows XP should
have UDF 2.01 support, although if you need to, fall back to 1.5 (-r

  E.g., typical external hd format command ...
     mkudffs --media-type=hd /dev/sdX#

  pktsetup -- shouldn't be needed for kernel 2.6 (although it depends on
kernel drive support), as the 2.6 kernel can packet write to many CD-RW,
DVD-RW and DVD+RW drives directly (direct DVD-RAM support has been in
since late kernel 2.2).

[ **NOTE:  Drive type is more of an issue with DVD support than the
drive media.  E.g., even if you use -R on a "dual format capable drive",
Sony/Philips +RW drives have a different command set than DVD Consoritum
-RAM/-RW drives. ]

Bryan J. Smith   mailto:b.j.smith@ieee.org
Some things (or athletes) money can't buy.
For everything else there's "ManningCard."

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