On Tue, Sep 05, 2006 at 11:24:52AM +0200, Geert Uytterhoeven wrote:
| On Tue, 5 Sep 2006, Phil Howard wrote:
| > On Sat, Sep 02, 2006 at 06:39:40PM -0400, Jon LaBadie wrote:
| > | It certainly would destroy one of amanda's features,
| > | the ability to easily recover backup data using
| > | standard unix utilities without amanda software.
| >
| > How is that destroyed?
| >
| > Suppose you use tar format. You can have tar read from tape directly,
| > which is what I presume you mean for being able to recover outside of
| > Amanda. You can have tar read from disk partitions if the native
| > partition scheme is used.
|
| At first I had the same reaction as you: it would work fine if you would cycle
| your tapedev through the partitions. However, then I realized a tape can
store
| multiple `files' sequentially, while a disk partition can't (without hackerish
| that would annihiliate the easy recovery again).
I beg to differ.
There are TWO ways to do this:
1. As a driver inside Amanda
2. As a driver inside the OS
Either way can do it exactly the same on disk. It requires the disk to be
fully dedicated to the backup, which is what you'd do for a tape, too.
The "tape file" would be a partition on disk. The two ways to implement it
would differ only in the mechanism of achieving it, but the end result would
be the same.
When writing first starts on the first "tape file", the first partition
is created on the disk and writing to it begins. The size of that
partition would be updated periodically, and definitely updated at the end
of writing the first "tape file". When writing the second "tape file", a
2nd partition is created. If the MSDOS partition style is used (supported
by numerous operating systems) the best approach would be to use extended
chaining as that can create an "infinite" number of "tape files".
Whenever a file on tape is overwritten, that file, as well as all that
follow it, would be "gone".
This could be a device driver in the OS designed to emulate fixed block
tape on a whole disk. The driver would remember which "tape file" it is
currently in, and handle the partitions accordingly.
This could be done in Amanda as a new raw disk driver with the logic to
effect the same thing as an OS tape-emulation driver would do.
As long as the OS supports the partition entries, which would be true for
a number of OSes, restore can be performed without Amanda AND without the
tape emulation driver in the OS, by having tar read from the respective
disk partition.
It might also be possible to do this entirely in user space without mods
to Amanda through remote (network) tape access.
| So as long as you dump only one DLE, it would work fine. If you dump more than
| one DLE, you need more logic.
More logic is a trivial issue when writing a driver.
--
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| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/ http://ka9wgn.ham.org/ |
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|
