Re: [Veritas-bu] How to plan out policy(schedules), [...]
2008-12-12 19:24:14
On Sat, Dec 13, 2008 at 10:31 AM, Curtis Preston <cpreston AT glasshouse DOT com> wrote:
Suit!?!?! Them's fightin'
words!
I need to do a blog on this, as I answer
this question a lot.
If you want to do weekly backups using
frequency based schedules, here are your choices.
- Leave
the window open only on the night you want the backup to run.
Schedules that succeed that night will be fine. BUT if it fails that
night, it won't retry until next week. Yuck.
- Leave
all nights' windows open. When the backup that's supposed to run
Monday fails and then runs on Tuesday, it will always run on Tuesday from
then on because that will be when it meets the frequency of 7 days.
Full backups end up creeping around and bunching together. I HATE
this one as it's unpredictable over time. I've seen it where over
time all my full backups were running on the same night. (I like to
spread them out.)
- Leave
a few days' windows open (say, 3), and set a frequency of 4 days. This
causes NBU to try on the first day with an open window, then retry on the
second/third if it fails. You have the retry feature that
calendar-based backups have without the schedule creep problem because you
have a frequency of four days. (This is the best of the three,
IMHO.)
The schedule-creep problem is compounded
by manual backups. If you ever do a manual backup, the frequency will be
calculated from that day. Suppose you chose option three above and opened
the windows for Friday, Saturday, and Sunday night, and put a frequency of four
days. If you happened to run a manual full backup on Thursday night, your
regular full backup won't run that weekend.
I agree 100% with Curtis on this. If you have a large environment with drives/resources being super utilised schedule creep can and is disastrous.
Not to mention client X expected his full to run on day Y and needed to backout from a change based on the full backup - woops!
_I_
like to do monthly full backups and weekly cumulative incremental
backups. The above problems are compounded when you want to do
this. You can't reliably predict what night the fulls are going to run,
and can't easily spread them out across the month (which I like to do).
It's much easier to spread them out using calendar based schedules. You
take some clients and tell them to do their full on the 1st Friday
of the month, and their cumulative incremental every Friday. When the two
"clash" on the 1st Friday, the full takes precedence and runs.
Every other Friday it will run a cumulative incremental. As for the
failed backup problem, you just check "allow after run day," and it will retry
the backups until they succeed, and this won't mess in any way with when
they'll run the next time. Also, running manual full backups won't mess
with the schedule either.
The manual tells you not to mix calendar
and frequency backups. I don't like calendar backups for daily backups,
so some see this as a problem. BUT I've found that if you monthly full,
weekly cumulative, and daily (frequency based) incremental all have the same
windows, the frequency-based schedule will take precedence and run when the
others aren't running and the calendar backups will take precedence when it's
time for them to run. You just have to keep the windows the same.
The only goofy thing about calendar-based
schedules (and it really annoys me) is that most people use a 6 PM to 6 AM
clock (or some evening hour to some morning hour). If you tell NBU to do
the full on the 1st Friday of the month and leave all windows open,
it will actually run the backup at just after midnight on Friday (Thursday
night). That's probably not what you wanted. So you have to delete
the window for the night before (in this case, Thursday). I hate it, but
I've learned to live with it.
Both methods have issues. I prefer
the predictability of the calendar-based method.
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