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Re: using disk instead of tape
2006-09-02 04:37:56
Phil Howard wrote:
What I would like to know is how Amanda handles backup to disk. I did find
a "file driver". I'm not sure if that is meant to be the "to disk" method
or not. It certainly would have some complications, depending on how one
considered disks as equivalent to tapes.
File driver is indeed what is used to perform backup to disk.
The complication would be the steps involved in handling a disk. I would
consider plugging the disk in (USB, Firewire, or eSATA) to be the rough
equivalent of inserting a tape into a manual tape drive. The question is
what will AMANDA do with a disk that has merely been plugged in. Can it
be configured to, or does it just understand that it needs to, mount the
disk? What if the disk is new and not yet formatted?
AFAIK, Amanda has no built-in functionality to handle removable disks. I
just wrote a little script for that purpose and it has worked quite
reliably for past two years.
Another note about comparing disk to tape from Amanda's POV - disks
(removable or not) are often handled not as individual tapes but as sort
of "virtual tape changer". The disk partition is divided into
subdirectories which Amanda handles as slots in a tape changer. I myself
use two removable disks, each holding 5 "slots" and only change the disk
once a week.
What it seems this "file driver" probably does not do, which a "disk driver"
(if such a thing exists) could do, is handle the disk as a raw device. It
could create a partition to be the equivalent of a tape file, and write the
dump/tar image directory to the partition sectors. When done (or when it
knows exactly how many sectors there will be), it could update the partition
table to represent the exact size. The next "tape file" could be written
after it and a partition table entry added for that partition/file.
That functionality (if it will be created) should IMHO be optional,
considering people who aren't using removable disks but for example just
one partition on their RAID. If I were one of such people, I wouldn't
feel too comfortable about Amanda re-writing my server's partition table
every day. It also seems to me that such functionality would need to be
programmed separately for each OS - quite a bit of work.
--
Toomas Aas
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