So now, if some of You are wondering what I'm actually trying to
do with Bacula Storage Solution - well I would say I try to
implement a straightforward ideal storage solution:
1. backups shall be saved to disk storage
2. disk storage shall be moved to tape after a certain time
3. tape storage shall be duplicated/mirrored
Concerning 1:
There are a lot of good reasons to save to disk.
- You do not need to change tapes
- The schedules will not interrupt unexpectedly for tapechange
- Restore does not need a tape to load and works much quicker
- You can increase backup frequency greatly, you could restore
an accidentally deleted file even if it was created only
half an hour earlier
- You can tune the volume size to your demands
Concerning 2:
There are no good reasons to keep older backups on disk.
- They are seldom required
- They occupy a *lot* of space, which can find better use
There are some more good reasons for 1+2:
- I am seldom and irregularly on-site. Nevertheless I want a
regularly scheduled backup - because when it is "manually
initiated backup", then it quickly becomes "no backup at all".
So the backup should go to disk, and when I'm on-site, I can
manually start the migrate-to-tape (which I MUST do because
otherwise the disk fills up).
- The tapedrives can be powered off. They are noisy, and they
add to the CO2 production.
- disk-buffering is implicite, so no "shoe-shining".
Concerning 3:
A tape cartridge is no more reliable than a disk.
Actually you SHOULD be able to restore most of the data even if
a piece of the tape is damaged, but with any modern tapedrive
I think if the header of the tape cannot be read in an orderly
fashion, then it gets similarly difficult as restoring from a
broken disk, i.e. it needs special facilities.
Now with disks it is totally convenient to have mirroring. Actually
I can choose for every filesystem if I want to take the space from
mirrored storage or from simple storage.
For tapes there is obviousely no way of *mirroring*, as they are
streaming devices. So there should be a way of duplicating,
if in realtime with two drives or sequentially with one does not
matter much, but with a finer granularity than image-copying
whole tapes, and someway managed by software, as it is really
boring to do this manually.
Now putting this into practice with Bacula gives a couple of issues,
which I am currently working on.
rgds,
PMc
--
..having tossedaway Microsoft(tm) already in 1991!
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