Hi,
Adam Goryachev wrote on 2009-08-17 13:15:59 +1000 [Re: [BackupPC-users] Feature
Requests and such?]:
> Clint Alexander wrote:
> > Hi BackupPC List Members (and owners)..
> >
> > One thing that has frustrated the heck out of me is the lack of finding
> > 1) I want to see *when* a backup is going to run. I've been making
> > changes to the overall schedule of the system, but it seems like all the
> > backups run in the last hour of the non-blackout times. I have 4
> > particular servers (SQL Cluster Nodes) that need to be backed up within
> > the same hour. I setup the blackout of these particular servers FROM 4am
> > TO 3am in hopes to get them done between 3-4am. But only one of them was
> > fired within that hour, the rest 2 hours later. So -- we should be able
> > to see what our current settings will do and when it will do it. I'm
> > sure there is a configuration that would work for this that I can't
> > figure out -- but it doesn't make the feature any less important :)
the problem is, that is not the way BackupPC works. BackupPC is very "dynamic"
about scheduling backups. From memory, at each wakeup, each host is scheduled
for a BackupPC_dump to be run. BackupPC then proceeds to run these as limited
by the MaxBackups setting. BackupPC_dump then goes on to determine if a backup
is actually necessary (and which type). Usually, most invocations of
BackupPC_dump will find that nothing is to be done (unless you really do a
backup of each host on each server wakeup). If we have MaxBackups = 2, and the
first two hosts are really due for a backup, then the check for the third host
will be done after the first of the backups completes. Again, a due backup may
complete very quickly, because the ping check fails (please note that this
cannot be determined ahead of time - you don't schedule hosts for crashing or
network links for breaking down, it just happens). So, if your wakeup was at
01:00, your third host might be checked at 01:54 - if the faster of your two
backups took 54 minutes to complete. The check might determine that a backup
is due, though at 01:00 it would not have been (when the check could just as
well have taken place). This makes a difference if 01:00 was the last wakeup
for the day (substitute a different value if that makes more sense to you).
The result of how BackupPC works is that it gets jobs done in a sane way
according to its configuration, if not always in an easily foreseeable order.
As has been said, if you have different requirements, schedule your backups
from cron.
>>From experience with a small scale setup (6 backed up hosts), I'd say it
works as expected (regular backups at the same time each day most of the
time). With 100 hosts, that is likely to be different.
> [...]
> Also, if your backups take 90 minutes each, then you get this:
> Backup 1 at 3am
> Backup 2 at 4:30
> Backup 3 at 6
> Backup 4 at 7:30
> All finished at 9am
>
> Now, the next day, the first backup won't start until 3am + 90min (4:30)
> + 0.97 * 24 = 3:47am or actually the first wakeup period after that
> which is probably 4am.
I don't think that is true. The startTime of the backup is considered, not the
endTime.
> As long as the blackout period covers more than 12 hours per day, you
> should get what you want (a backup starting as close as possible to the
> beginning of your non blackout window, and a backup every non-blackout
> window (daily).
Just note that the blackout window is not mandatory. It will only be taken
into account as long as the host doesn't fail ping checks.
Regards,
Holger
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