2009-11-16 11:09 AM
Can anyone shed a light on this? I know what snapshot is, but never understood the diifferent between nightly and weekly.
if i do a snap list, i would see 5 nightly and 1 weekly. is weekly = full backup and nightly = incremental backup like how backups to tape is handle?
greatly appreciate the help.
2009-11-16 12:08 PM
There is no technical difference in a nightly snapshot and a weekly snapshot. The difference here is that you can have different retention for nightly vs weekly. So I can keep 6 nightly snapshots and 8 weekly snapshots for example. In either case, the snapshots appear as full backups of the volume even though space consumption is made up of only changed data since the snapshot was taken. No data is copied when a snapshot is created, and this is much different than the traditional tape full / incremental way of thinking.
Hope this helps!
2009-11-16 12:15 PM
Also if both weekly and nightly snapshots are scheduled at the same time on any day, the snapshot created at the time specified is labeled weekly and no nightly snapshot is retained for that time.
2009-11-17 03:38 AM
Automatic snapshots can be scheduled to occur weekly, daily, or hourly. Weekly snapshots are named weekly.N,
where N is "0" for the most recent snapshot, "1" for the next most recent, and so on. Daily snapshots are named
daily.N and hourly snapshots hourly.N. Whenever a new snapshot of a particular type is created and the number of
existing snapshots of that type exceeds the limit specified by the sched option described below, then the oldest
snapshot is deleted and the existing ones are renamed. If, for example, you specified that a maximum of 8 hourly
snapshots were to be saved using the sched command, then on the hour, hourly.7 would be deleted, hourly.0 would be
renamed to hourly.1, and so on. If deletion of the oldest snapshot fails because it is busy, the oldest snapshot is
renamed to scheduled_snap_busy.N , where N is a unique number identifying the snapshot. Once the snapshot is no
longer busy, it will be deleted.
2009-11-17 05:35 AM
I can see where the confusion is coming from, as daily incrementals and weekly full backups are a backup schedule common to most people.
The key point for me is understanding what the snapshot is and then what it is called. As you've said that you understand what a snapshot is, lets not go over it, but look at what it's called.
They could be called anything. You could have a snaplist of "just_before_lunch.0, delete_that_line_in_accounts_sheet.1, bob_on_holiday.2" as they are only points in time.
Some confusion can come when you see daily.0, daily.1,daily.2,daily.3, daily.4, weekly.0 which can look like daily backups for all working week days and a full backup on the Saturday, but as stated above, it's just a name from a time stamp that the snapshot was taken, no different from any of the others.
If you have weekly.0 (Monday 1st) and weekly.1 (Monday 8th) on a weekly snapsnot schedule and then you create a file on Tuesday 2nd and delete it on Wednesday 3rd, it's gone. There is no snapshot to call it back from.
Hourly, daily or weekly, is just the frequency with which you take your snapshots and how far back in time you can go.