Re: Defect management with DVD-RAM on Linux?
Hi,
> 1) It is still possible that I have overlooked some obscure mount
> option, which turns on write verification for DVD-RAM drive.
The default SCSI write command behavior on
DVD-RAM is with Defect Management. (For what
it is worth at all.)
I deem it unlikely that the kernel circumvents
it when doing random read-write i/o.
Afaik, growisofs refrains from using the
special command and options which would
disable Defect Management and yield the
nominal write speed of the media.
My own programs offer this as option.
> 2) There could be some other software solution
Rather not.
The problem is that the Defect Management
acts at write time, while you want to see
your data some time later.
If not the kernel used WRITE12 with Streaming
Bit then it wrote with Defect Management and its
immediate verify reading did succeed.
With DVD-RAM this is traditionally no quarantee
for flawless reading some minutes later.
Effective write speed should indicate the
presence of Defect Management.
1x DVD = 1.3 MB/second. If your media writes
with half or a third of its nominal speed
then Defect Management is active.
If it reaches full speed as advertised by
the manufacturer then Defect Management is
disabled.
(You need to flush the write buffers for a
realistic speed measurement.)
> 3) Should I submit a bug report/feature request?
Rather not.
You could ask at LKML whether they use SCSI
command AAh WRITE12 with Streaming Bit.
(My bet: they don't)
> Though I use ubuntu, rather than debian,
This list is for any burn topic. At least with
open source stuff on open source systems.
For proprietary stuff there are other forums.
> When I chose DVD-RAM as the backup media for my data, the important
> factor was built-in hardware defect management.
To my experience reliability of DVD-RAM is inferior
to DVD+RW. Other disadvantages are speed and media
capacity.
More interesting are BD-RE which have the same
advertising promises but seem to work much more
reliably than DVD-RAM.
But - after half a year of two daily backups -
the slow Defect Management used not a single
spare sector and readability seems worse than
with the other BD-RE which i run without
Defect management. (Guessed from read speed
when checkreading.)
> growisofs or something alike is
> necessary to place the data to the medium, which is not very
> convenient.
But our usage model is known to work.
Random access writing to optical media is
in best case darn slow. Normally it makes
trouble since the days of Mt. Rainer
formatted CD-RW.
For backup purposes you normally want the
most reliable write method and have few
reason to frown on our streaming.
My preferred backup media are DVD+RW and BD-RE
(without Defect Management).
I do a checkread after the backup and if the
media is slow or even faulty, then i repeat the
backup immediately with other media.
This strategy works as long as failures are
rare. Well, for now they are rare.
Have a nice day :)
Thomas
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