Re: Writing Dual Layer DVD-RW using Linux
Hi,
> I use a 10GB HP Colorado tape drive to backup my personal Linux PC
> every week/month. I backup to the tape using GNU tar in compress mode,
> thereby allowing me to back up to approximately 20GB of files.
>
> The closest alternative to the 10GB tape is the 8.5GB DVD-RW DL (i.e.
> dual layer). The capacity should be good enough for my needs.
>
> I can't write to a file on hard disk and afterwards burn the DVD as I
> do not have enough disk space. So, I am thinking of using the kernel's
> packet writing abilities to do my backups.
This list is probably not the right point to find
expertise about the packet interface and UDF.
We are more into burn programs which write whole
sessions in a single sweep.
Linux packet writing relies on a particular write
strategy which is not necessarily available with
all media types or media states.
Wether it will work with DVD-RW DL is a matter of
trying out. Tell us, so we can tell the next one.
Are there really -RW DLs ? MMC-5 lists
DVD+R DL, DVD-R DL, DVD+RW DL.
I never saw DVD+RW DL on sale, btw.
The fact that you will be writing your archive
on-the-fly is not necessarily an obstacle to our
style of burning. The typical problem with that is
that some programs with some media demand a
predicted size.
But with few media types and states this size
prediction is really inavoidable.
If your media supports packet writing then i am
quite sure it will do writing on the fly via
program growisofs.
Like
tar -jcf - * | \
growisofs -Z /dev/hdc=/dev/fd/0
(/dev/hdc is the target drive, /dev/fd/0 is
standard input to be used as data source.)
You need no other preparations for that.
The tar archive can later be read from not mounted
/dev/hdc like from a tape at /dev/mt0.
Maybe you get error messages about an unclean
end of archive because of extra bytes.
(afio and star archives do better.)
If it turns out that DL media are not suitable
then i would advise you to use DVD+RW.
It is not too hard to split a tar archive over
several media but i am more in favor of producing
an independent archive per media.
For that i have my own backup tool scdbackup which
can produce afio or star archives and puts them
on a set of media (CD, DVD, ...).
growisofs is used as burn program for DVD media.
Since the size is unpredictable it is estimated
cautiously and an eventual overrun is handled by
writing the rest to another media.
It is also able to make one big archive which gets
split over several media. But reading those is
cumbersome because you have to read the whole
media set in order to access a file on the last
media.
For quickest file access i prefer scdbackup's
ISO-9660 formatted output. This cannot be compressed
but if you need to access a single file it is
unbeatably convenient.
If you backup whole partitions or exotic file
types, i would advise to use afio or star format.
Many media types do not produce a neat End-Of-Media
event. So the archive formats have to provide own
means to detect their End-Of-Archive.
To my experience GNU-tar fails to do so.
That's why i deem afio and star more suitable.
Each of them has its strengths:
afio -Z has its archive structure uncompressed
but the files are compressed. This allows to
recover sane parts of damaged compressed archives.
star is very complete when it comes to file types
and sizes. I use it for system snapshots made from
single user mode or a booted rescue system.
Restore works like that: boot rescue system,
make empty filesystem, unpack archives to filesystem,
eventually update boot loader (run /usr/sbin/lilo),
boot.
(Of course this works only if you can continue
using your old system hardware configuration.)
I never challenged afio like that. It is not outruled
that i produces sufficiently complete system
snapshots too.
Have a nice day :)
Thomas
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