RE: EXTERNAL: Re: Problem with growisofs -- cannot write multisession DVDs without ejecting and reloading tray
Hi Thomas,
As always, thank you for your helpful responses.
> The new session adds a new superblock, a new complete directory tree, and the content of data files which were newly added or overwritten by the session.
Ohhhh that makes sense. I was thinking that the entire DVD had one superblock at the beginning, and that couldn't be right, because how would it get updated?
> But as said, mounting older sessions imight be desirable with incremental backups. E.g. if i want to mount the backup state of three days ago,
I hadn't thought of that as a possible use. We always date our backups and log files in the filename, so if we want an older one we just go to the file with the correct date.
A couple more questions:
I am trying to figure out if I can close a DVD without writing a new file to it. I searched the man page and came up with:
xorriso -dev /dev/sr1 -close on --
This looks like a good command -- it doesn't spit out errors as such -- but it doesn't do anything. I can still append data to the medium, so it didn't close the disk. But, if I write a file, as in:
xorriso -dev /dev/sr1 -close on -add closeme.txt --
Then the medium gets closed, and I can no longer write to it. Is this the only way to close the disk? That is, do I have to write some file if I arbitrarily decide it's time to close the disk?
Also, about status. You said:
> The number of sessions on DVD-R is restricted to 99, on DVD+R the limit is 153.
This is very helpful to know, when combined with the number of tracks I have written. I figured out that:
xorriso -dev /dev/sr1 -status short
will give me the status that a normal write prints out without having to write anything, which is useful. It tells me how many sessions are on the disk, and how much space has been used (including padding), and how much space is left. My question is, is there a way to get the number of session left for the medium? Short of manually subtracting the number of sessions on the disk from 99, that is.
Thanks, and have a great day,
-Eric J. Richardson
-----Original Message-----
From: Thomas Schmitt [mailto:scdbackup@gmx.net]
Sent: Wednesday, May 13, 2015 12:23 AM
To: cdwrite@other.debian.org
Cc: Richardson, Eric J
Subject: EXTERNAL: Re: Problem with growisofs -- cannot write multisession DVDs without ejecting and reloading tray
Hi,
> > OpenSolaris snv 134 always mounts the youngest session.
> You'll have to forgive me, but I don't know what this means. Would
> that mean that only the last files written can be seen, or all of them?
You see all files which you added (and did not delete later).
The capability to access older states is interesting with incremental backups.
ISO 9660 multi-session works like this:
The new session adds a new superblock, a new complete directory tree, and the content of data files which were newly added or overwritten by the session.
The older superblocks and directory trees still exist on the disc. They may point to older versions of files which got replaced by other content in further sessions, and they may contain files which were deleted from the directory tree of the younger sessions.
Operating systems by default use the youngest superblock and directory tree for mounting.
But as said, mounting older sessions imight be desirable with incremental backups. E.g. if i want to mount the backup state of three days ago, i put in my backup BD-R and do
xorriso -indev /dev/sr2 -toc
which tells me
TOC layout : Idx , sbsector , Size , Volume Id
ISO session : 1 , 0 , 1461973s , HOME_2015_01_05_130954
ISO session : 2 , 1462144 , 53613s , HOME_2015_01_06_114520
...
ISO session : 126 , 8364224 , 54847s , HOME_2015_05_10_113721
ISO session : 127 , 8419232 , 62170s , HOME_2015_05_11_120517
ISO session : 128 , 8481568 , 63170s , HOME_2015_05_12_135346
Media summary: 128 sessions, 8544896 data blocks, 16.3g data, 7177m free
If i then execute (on Linux)
mount -o sbsector=8364224 /dev/sr2 /mnt/iso
i get to see the backup state of may 10 2015, 11:37:21.
There is some convenience built in. The run
xorriso -mount_cmd /dev/sr2 volid '*_2015_05_10_*' /mnt/iso
on Linux makes this proposal of a mount command:
mount -t iso9660 -o nodev,noexec,nosuid,ro,sbsector=8364224 '/dev/sr2' '/mnt/iso'
On FreeBSD the proposal would rather look like
mount_cd9660 -o noexec,nosuid -s 8364224 '/dev/cd1' '/mnt/iso'
A privileged user may also do
xorriso -osirrox on -mount /dev/sr2 volid '*_2015_05_10_*' /mnt/iso
and have the proposed command executed directly by xorriso.
(One still has to umount manually, when done.)
My backup sessions got their volume ids with time stamp by xorriso command
-volid HOME_"$(date '+%Y_%m_%d_%H%M%S')"
when the backups were made. (See man page example "Incremental backup of a few directory trees".)
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