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 -- To UNSUBSCRIBE, email to [email protected] with a subject of "unsubscribe". Trouble? Contact [email protected]
