Defect management with DVD-RAM on Linux?
Hi, everybody!
When I chose DVD-RAM as the backup media for my data, the important
factor was built-in hardware defect management.
So I took for granted, that any OS which supports UDF writing, should
also support automatic verification and reallocation of bad blocks.
However, I recently has tried to copy a huge (about 4Gb file) database
backup (Ubuntu Linux Server 8.04.3 , mount /dev/dvdram /mnt/dvdram &&
cp /backup/hugefile /mnt/dvdram) I got a non-readable target file.
dmesg output contained lines like
[345555.460831] Buffer I/O error on device sr0, logical block 54040
When I tried to copy smaller files (10-200Mb) to the disk - some of
them copied OK and other still contained errors. Not every block of
the medium was bad!
I googled a bit and found a following note in the file
http://www.kernel.org/doc/Documentation/cdrom/packet-writing.txt
> Packet writing for DVD-RAM media
> --------------------------------
....
>
> - Defect management (ie automatic remapping of bad sectors) has not
> been implemented yet, so you are likely to get at least some
> filesystem corruption if the disc wears out.
>
BTW, I do not use pktcdvd (according to lsmod it is not loaded). But
if the quoted phrase is earnest, it ruins my assumption that DVD-RAM
is a robust backup medium on linux. If pktcdvd states that it does not
support DVD-RAM defect management, then udf driver may also fail to
support it. And my experience seems to confirm this assumption.
Some software packages for Linux (e.g. DVD+RW Tools) explicitly state
that they do support defect management for BD and DVD-RAM. But those
packages do not offer random access - growisofs or something alike is
necessary to place the data to the medium, which is not very
convenient. Still, it means that bad sector remapping for DVD-RAM is
feasible in linux. So why it is not presently implemented in kernel
modules?
My questions to the community are:
1) It is still possible that I have overlooked some obscure mount
option, which turns on write verification for DVD-RAM drive.
(Something similar to "verify on" of ancient DOS days).
Does anyone know if there is something of the kind?
2) There could be some other software solution on Linux that supports
DVD-RAM defect management while giving random write access to the
media. Even a proprietary solution if it is of good quality and not
too dear. Any ideas?
3) Should I submit a bug report/feature request? What is the most
effective place to file such a request? (Linux kernel development,
Debian of Ubuntu development, what could you suggest?).
Thanks for everyone who bothers to read this.
Yuri Baranov
PS Though I use ubuntu, rather than debian, I assume that the problem
may relate to different linux distributions.
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