Cumulative Incremental Backup behaves as Differential Incremental Backup

[Jaap_Hartog]

Hi All,


first some statistics:
Veritas NetBackup 6.5.3
Quantum i500 Tapelibrary
Separate Master-, Media- and BMR Bootserver, running with Windows 2003

We run Full Backups of our NAS in the weekend, starting on Friday, all other weekdays (Mo-Tu-We-Th) we run Differential Incremental Backups.
These Differential Incremental Backups average 2,2 tapes per day, effectively costing 3 tapes per day. To work more cost-effective with a certain number of tapes,
we thought of switching over to Cumulative Incremental.

In the weekend of 28-29 November I modified our existing Differential Incremental schedule.

I did this as follows:
I converted the existing diff-schedule to Cumulative Incremental, adjusted the number of days to 3 and removed the Thursday-schedule part.
Next I copied this Cumulative Incremental schedule, moved the Wednesday-schedulepart to Thursday, removed the other days and put the frequency to weekly.

The old Schedules:


The new Schedules:


The Schedule Dialog Box for the first 3 weekdays:



And for the last weekday, Thursday:



The effective set of Incrementals would thus be produced on Thursday, after which the other backups (Mo-Tu-We) could  be expired.
Our expectancy about the number of used tapes would be like
Mon:    3
Tue:     <3 (Mon) + 3
Wed:   <3 (Mon) + <3(Tue) + 3 (Wed)
Thu:    <3 (Mon) + <3(Tue) + <3 (Wed) + 3

But since the modification, the production was still similar to the previous situation (Differrential Incremental), yielding 3 tapes each day, also on Thursday.
So all labels and titles tell me that the Incremental Backup is Cumulative now, but the number of tapes tells me something different.

Even in the BAR, the corresponding colour of the images has changed:

Furthermore : if I want to trial-restore a file, modified on monday,  a monday-tape is needed.
I would have expected the need for a thursday-tape, containing the total of incrementals of the entire week.

Have I omitted something, causing the Incremental Backup still to behave as a Differential one ?

All advice is greatly appreciated !

Kind regards,

Jaap Hartog

[petejb]

Hi,

Firstly, it may be worth noting that the terminology that Symantec Netbackup is using for the type of backup may be confusing and it is different to normal terminology and the other way round from a traditional sense.

Normally, you would have a Differential which is everything since the last Full Backup and Incremental for everything since the last backup of any type (normally the Incremental). So you would need the Full Tape and the last Differential for a restore, or the Full Tape and ALL the Incrementals for a restore.

In Symantec Netbackup it is the other way round.

A cumulative incremental backup backs up the files that have changed since the last full backup. All files are backed up if no previous backup has been done. (More like a Traditional Differential).

A differential incremental backup backs up the files that have changed since the last successful incremental (differential or cumulative) or full backup. (More like a Traditional Incremental)

I mention this as the driving force was to attempt to save tapes so in the long run using the cumulative incremental (if lots of data is changing) will use more tapes the longer it runs (So you may see Mon 3 tapes, Tue 3 tapes , Wed 4 tapes , Thu 5 tapes) as it is performing a Differential.

This may account for the tape confusion when you are attempting to restore data.
That is how I am reading your post anyway.

Hope it helps.

 

[Jaap_Hartog]

petejb,

to explain it a bit better:
when using Diff. Inc.: we were using appr. 3 tapes a day but not filling 3 tapes a day (at least 1 tape is not filled entirely, and that happens 4 times a week)
when using Cum.Inc : we should be using an increasing amount of tapes -like you mentioned 3-3-4-5- , of which we only keep the last set. Of this last set, only one tape is not filled entirely. There is less waste.

But actually, we are still using 3 tapes a day, and the amount of new/modified data on our storage hasn't changed.
According to Netbackup, Cum. Incr. is active (see all pics above) but the amount of used tapes says something else ...
The policies, containing the diff schedules have been deactivated.

Can it be that Cum. Incr. doesn't work well with NDMP ?

[J_H_Is_gone]

Incrementals based on timestamp

Specifies that files are selected for the backups that are based on the date that the file was last modified. When Use change journal in incrementals is selected, Incrementals based on timestamp is automatically selected.

Incrementals based on archive bit

Specifies that NetBackup include files in an incremental backup only if the archive bit of the file is set. The system sets this bit whenever a file is changed and it normally remains set until NetBackup clears it. A full backup always clears the archive bit. A differential-incremental backup clears the archive bit if the file is successfully backed up. The differential-incremental backup must occur within the number of seconds that the Wait time before clearing archive bits property indicates. A cumulative-incremental or user backup has no effect on the archive bit. Disable this property to include a file in an incremental backup only if the datetime stamp for the file changed since the last backup. For a differential-incremental backup, NetBackup compares the datetime stamp to the last full or incremental backup. For a cumulative-incremental backup, NetBackup compares the timestamp to the last full backup. If you install or copy files from another computer, the new files retain the date timestamp of the originals. If the original date is before the last backup date on this computer, then the new files are not backed up until the next full backup. Note: Symantec recommends that you do not combine differential incremental backups and cumulative incremental backups within the same Windows policy when the incremental backups are based on archive bit (default).

[Jaap_Hartog]

Mr. Hinchcliffe,

the storage that we are talking about is an EMC-NAS.
It runs with a Linux-OS, and we use NDMP to be able to back it up.
Due to the fact that it is not a Windows-client, we cannot obtain client settings-information and change settings for Incrementals as shown in your picture.
I have witnessed that Incrementals are not being made based on archive bit, but based on timestamp, since the archive bit is not cleared from files, beaing the archive bit.
I have been told this also by a Symantec Consultant...

So I guess that archive bits are not the issue....

Kind regards,

Jaap Hartog