The requirement for 2 drives is not mandatory, it ought to be just a
suggestion. LTO can be used as a standalone drive, TSM can use single
drive or small autoloader with single drive. So it is NOT required but
recommended.
For business reasons it may be necessary to have 2 or even more drives.
Others already pointed reclamation and off-site copying problems you may
have. They can be worked around but again you have to compare performance
and total costs
single drive reclamation - define reclamation storage pool of type FILE.
On reclamation remaining data is moved to files and later written to new
tape volume. Drawback: data is not read when written (sequential
read+write vs. parallel) thus takes more time. Calculate time budget
around the clock.
single drive copypools - define following hierarchy DISK -> FILE -> LTO
(file pool would be also lto reclamation pool). Prevent file->lto
migration during backups (highmig=100). Perform backups to copypool after
node backups finish. Allow migration after backup to copypool finishes.
Drawbacks: filepool must be large enough to hold all backups data. Backups
should not happen during migration because some object(s) may migrate
without being copied to the copypool. Again time - data have to be written
twice through the one-and-only drive. And on the end with one drive there
is no way to perform copypool reclamation.
Conclusion: for a small installation data might be not too much, time
might be enough for all activities (node backups, copypool backup, primary
pool raclamation, migration, DB backup). Thus neither LTO technology nor
TSM dictate number of drives to be used but only the business requirements
you have.

Zlatko Krastev
IT Consultant




Please respond to "ADSM: Dist Stor Manager" <ADSM-L AT VM.MARIST DOT EDU>
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Subject:        2 drives are required for LTO?

One of the System Admins has been talking to an IBM
Business partner and was told, apparently, that the
use of two drives is not only recommended but is also
required with LTO. Is this true? If so, why?

I checked out
http://www.tivoli.com/support/storage_mgr/devices/lto.html#notes
and noticed that some LTO libraries are noted A/E
meaning that Advanced Managed Library feature" is
required? Is there a technical reason for this?



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