On Fri, Aug 08, 2003 at 02:44:22AM -0400, Sarah Nordstrom wrote:
> I'm setting up Amanda here, and would like someone with a bit more
> experience than me to look over this and say if it looks decent. I'll
> have someone (me :) ) onsite 4 days out of every 8 to change tapes
> (i.e. days 1-4 tape changes can happen, days 5-8 tape changes will not
> happen), which is not ideal, but that's how it's going to work out.
> I'm thinking that I can run backups to tape the 4 days when changes
> happen, and let backups build up in the holding disks on days when
> tapes do not get changed? The plan right now is for an 8 tape set,
> what determines the best dumpcycle to use?
The value and importance you place on your data. A dumpcycle is how
frequently you want a particular DLE (disk list entry) to get a full,
level-0 backup rather than an incrementals of changes from the last
level-0.
Certainly everyone feels their data is absolutely priceless :)
I need everything backed up fully each hour!!!
So that has to be tempered with reality. How much total data do you
have? How big is your tape and how many can be used for a single
dump? How much holding disk do you plan to devote to your backups?
Suppose you have 1TB of data (not disk space, likely data to backup)
and are using a tape with a 100GB native capacity, only one allowed
per backup. That tape might hold with compression 150 - 200Gb.
Using the lower number, 1000GB total / 150GB per backup max, you can't
go with a number of amdump runs per dumpcycle of less than 7. So
your "runspercycle" parameter must be at least 7 (no units, just 7).
It seems you are planning on running amdump daily, so any number of
days greater >= runspercycle would be doable for amanda. But suppose
you were only running amdump 5 days a week (business days), then you
would have to use a longer dumpcycle to accommodate your 7 runspercycle
requirement, maybe 14 days or some in-between number like 10 days.
Then there is the question of how many tapes you will be cycling through.
An absolute minimum number is runspercycle. That works if nothing ever
goes wrong goes wrong goes wront goes wron... Runspercycle + 1 is really
the minimum, (Runspercycle * 2) + 1 is my recommended minimum. I'm using
4 * runspercycle and with a dumpcycle of 1 week so I maintain a month's
worth of backups available for recovery. BTW the number of tapes actually
being "cycled" and your tapecycle parameter don't have to match, the
'tapecycle' parameter is the minimum number you can cycle through.
And for holding disk space, allocate gobs. Amanda doesn't use any it
doesn't need and it can also serve other applications. BTW you can
define multiple holding disks, not just one. I define 3, all the extra
space on 3 large FS's except telling amanda not to use the last 0.5GB
of each. But each holding disk you define should be on a separate
physical drive. Doesn't have to be, but better to avoid disk thrashing.
You will need, as an absolute minimum, enough for five plus dump runs;
the four that collect while you are off-site plus that days' plus some
for spare change for unusual times. Even though I do dumps 6 days a
week, my 3 HD's can cope with about 15 - 20 amdumps. So if I forget
to change my autoloader magazine some week and go on vacation, amanda
can cope and run normally until my return. Otherwise it would go into
"degraded" mode where only incrementals are done because there is little
holding disk space available. That is the "spare change" and is defined
by the "reserve" parameter as a percentage of the total holding disk
space. Note, it defaults to 100% and you will undoubtedly want to set
it lower.
>(By the way, an autoloader
> is out of the question for now.. eventually, this will likely be the
> best solution though.. someone needs to invent an autoloader that'll fit
> in a 1U box ;) )
If you trust disks, I suppose you could get several hard disks
in a 1U box and do backups to disk with the file:driver. That
can "autoload" for as many "tapes" as you wish. Of course you
are already planning on trusting your disks for half of your
backups. Maybe you should do all of them to disk.
> Any comments appreciated :)
>
Hope these helped.
--
Jon H. LaBadie jon AT jgcomp DOT com
JG Computing
4455 Province Line Road (609) 252-0159
Princeton, NJ 08540-4322 (609) 683-7220 (fax)
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