On Sat, Sep 02, 2006 at 06:39:40PM -0400, Jon LaBadie wrote:

| Phil,
| what advantage(s) do you forsee in amanda's use of raw disk
| devices as opposed to files on the native filesystem.

The ability to avoid the page cached I/O subsystem to control
performance impact on the system.


| 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.


| I've not heard people on the list reporting poor performance
| in using the current scheme for saving backups on disk-based
| 'virtual tapes'.  If there are, I'd like to know about it.

How could they have compared if there is none writing to raw disk now?


| Given that the backups are coming from dump or tar, possibly
| over a network, possibly processed by compression and encryption
| software, it is unlikely that the final disk writing is a bottleneck.

Certainly there will be situations where other factors affect the speed.


| Perhaps additional features would be possible.  Like multiplexed
| "direct to tape" dumps without a holding disk.  The current scheme
| only allows a single dump direct to tape.  Multiplexed dumps have
| to go to a holding disk before being taped.

A potential project will have some very large data.  Each machine can
have its own external backup drives, so for each machine it can be seen
as a single dump.  It's just going to be large.  Probably 400G or 800G
per machine.  I'm just exploring all options and Amanda is one of them.
If I do go with a filesystem on the disks, I'll probably use rsync so
the disk is a replica and can simply substitute as is.

-- 
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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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