Eric Sproul wrote:
The most crucial options are dumpcycle (how long it takes to get through
all your tapes) and tapecycle (the total number of tapes to be used).
A little nitpicking here. Dumpcycle is how often you want a full dump
of everything (that's exactly what you state below :-)); it is best to
have dumpcycle much less than tapecycle, so that you have more than one
full dump of each DLE somewhere on tape.
Dumpcycle is measured in days or weeks (days*7).
Tapecycle is measured in tapes.
And runspercycle is just a number (I wonder why Redhat puts the unit
"weeks" here in their default config?)
AMANDA will ensure that all of your filesystems get a full backup once
per dumpcycle, and tapecycle lets AMANDA know when to cycle back around
to the first tape. The above documentation will help you compute your
dumpcycle.
For example, I have a 24-slot changer, and I run AMANDA daily, so my
dumpcycle is 24 days. Since I want to keep as much history as possible
Even with a 24-slot changer you could have a dumpcycle of e.g. 12 days
or 6 days (or 23 days or 5 days - it doesn't need to be a multiple
either). The constraints are: for shorter dumpcycles, amanda has to
put more full dumps on each tape, resulting in fuller tapes and longer
backup time; for longer dumpcycles, amanda probably needs to put higher
levels of incremental dumps, resulting in longer restore time, and less
redundancy of full dumps.
It's best to make your dumpcycle as short as comfortable: runtime
each night, tape capacity, and comfort for restoring (did you ever
recover something from a level 5 incremental backup using a slow
DDS2 drive? :-)
Just nitpicking of course...
(to the limit of my budget!), I choose to have a second set of 24 tapes,
so I get to keep two complete dumpcycles (48 days' worth). This makes
my tapecycle 48 tapes.
--
Paul Bijnens, Xplanation Tel +32 16 397.511
Technologielaan 21 bus 2, B-3001 Leuven, BELGIUM Fax +32 16 397.512
http://www.xplanation.com/ email: Paul.Bijnens AT xplanation DOT com
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