Hi I am trying to make Bacula work with my DVD+RW and DVD-RAM media, as raw devices (similar to tape, but with random r/w support, which speeds up appending and lseek64()ing to restore files). I have tested the access method to properly work on Linux 2.6.x and NetBSD, and have been using this method for other data archival purposes for a while. Other OSes should support this seamlessly, as even Windows supports writing DVD-RAM without the need of specialized applications or drivers.
I have included some test runs with 'dd' utility, as it is easily understood and versatile enough to provide the actual tests, proving that such access is viable. I have included only the NetBSD version of the test, but should you require it, I can provide the Linux version as well. Motivation: - I feel that accessing the device directly, just like Bacula does to tape devices, is a better way to handle backups. - There are some restrictions with appending a new ISO9660 session for each append to the disk, one of them being able to correctly append data to the SAME volume (no need to create ANOTHER file on the disk to hold extra data) - Even if negligible, creating a new session wastes some disk space - Support for multiple sessions varies in implementation quality across platforms (I recently had trouble recovering data from a multi-session volume on a Debian system, and such data was available when mounted on NetBSD, Windows and Slackware), but I expect "reading raw data from the disk" to be portable across different OSes. - I read on the lecture slides by *Kern Sibbald for *UKUUG that one of the goals of the project is "assure data compatibility for 30 years (providing you have the appropriate hardware)". It seems logical to me that the less software layers we need to ensure that, the better, so raw device is _my_ logical choice. (Even though DVD+RW might be low-quality media, DVD-RAM is higher quality and is supposed to have much higher shelf time. There are some manufacturers supposedly claiming 50 year archival lifetime for DVD+RW already, so it might be worth considering.) - Specially on Linux, I have big performance improvements whenever I use raw devices instead of files within filesystems, for whatever reason. This applies to Databases, Virtual Machine images, and other data as well. - Avoid Data Spooling - Avoid the overhead of flowing all the backup data through a preprocessor (mkisofs, for instance), saving sometimes precious CPU cycles in these days of virtualized servers. The following scenarios list my test experiences with Bacula 2.2.4 on NetBSD (I can, again, provide results with a more recent build if necessary) Case 1: Device Type = DVD Archive Device = /dev/cd0d Random Access = Yes; RemovableMedia = yes; RequiresMount = no; # MountPoint = # MountCommand = # UnmountCommand = # SpoolDirectory = # WritePartCommand = # FreeSpaceCommand = result: goldstein-sd ERROR TERMINATION dev.c:195 Mount and unmount commands must defined for a device which requires mount. Case 2: Device Type = Tape Archive Device = /dev/cd0d Random Access = Yes; RemovableMedia = yes; RequiresMount = no; # MountPoint = # MountCommand = # UnmountCommand = # SpoolDirectory = # WritePartCommand = # FreeSpaceCommand = result: goldstein# btape -v /dev/cd0d Tape block granularity is 1024 bytes. btape: butil.c:285 Using device: "/dev/cd0d" for writing. 19-Nov 23:05 btape: Fatal Error at device.c:296 because: dev open failed: dev.c:422 Unable to open device "DVD Writer" (/dev/cd0d): ERR=Bad file descriptor 19-Nov 23:05 btape: btape Fatal error: butil.c:194 Cannot open "DVD Writer" (/dev/cd0d) Case 3: Device Type = File Archive Device = /dev/cd0d Random Access = Yes; RemovableMedia = yes; RequiresMount = no; # MountPoint = # MountCommand = # UnmountCommand = # SpoolDirectory = # WritePartCommand = # FreeSpaceCommand = result: Sending label command for Volume "TESTE" Slot 0 ... 3910 Unable to open device "DVD Writer" (/dev/cd0d): ERR=dev.c:480 Could not open: /dev/cd0d/TESTE, ERR=Not a directory For the following tests, the disk was forced to SPIN DOWN before the beginning of each run and block sizes were chosen at random, so real-world speeds should be way greater. Small test to demonstrate the RW nature of the device, and the ability to work with offsets (expected from DVD+RW and DVD-RAM media, unexpected otherwise) goldstein# dd if=/dev/urandom of=1mfile bs=2k count=512 512+0 records in 512+0 records out goldstein# dd if=./1mfile of=/dev/cd0d bs=2k seek=2 512+0 records in 512+0 records out 1048576 bytes transferred in 0.774 secs (1354749 bytes/sec) goldstein# dd of=./1mfile2 if=/dev/cd0d bs=2k skip=2 count=512 512+0 records in 512+0 records out 1048576 bytes transferred in 0.919 secs (1140996 bytes/sec) goldstein# cmp ./1mfile ./1mfile2 || echo differ goldstein# Test to demonstrate the random access of the device, as expected from DVD media. goldstein# dd if=/dev/cd0d bs=1m seek=500 count=1 of=/dev/null 1+0 records in 1+0 records out 1048576 bytes transferred in 1.247 secs (840878 bytes/sec) goldstein# dd if=/dev/cd0d bs=1m seek=700 count=1 of=/dev/null 1+0 records in 1+0 records out 1048576 bytes transferred in 1.518 secs (690761 bytes/sec) Test to demonstrate the random WRITE access of the media (expected on DVD+RW and DVD-RAM, unexpected otherwise) goldstein# dd if=/dev/urandom bs=1k count=1 of=/dev/cd0d seek=100000 1+0 records in 1+0 records out 1024 bytes transferred in 3.046 secs (336 bytes/sec) goldstein# dd if=/dev/cd0d bs=1k skip=100000 count=1 | hexdump -C 00000000 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................| * 00000400 1+0 records in 1+0 records out 1024 bytes transferred in 0.001 secs (1024000 bytes/sec) Thanks for considering the idea Evaldo Gardenali ------------------------------------------------------------------------- This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK & win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100&url=/ _______________________________________________ Bacula-users mailing list Bacula-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/bacula-users
