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Incremental File Selection Issue

CypSteel
Level 2

I recently was moved to our backup and recovery team to help cleanup, standardize, and follow best practices in our NetBackup enviroment.  One of the things that seemed incorrect was the use of incremental policies.  By definition from the software:

Cumulative Incremental Backup: Backs up the files that are specified in the backup selections list that changed since the last full backup. All files are backed up if no previous backup was done. Cumulative incremental backups occur automatically according to schedule criteria. A complete restore requires the last full backup and the last cumulative incremental backup.

Differential Incremental Backup: Backs up the files that changed since the last successful incremental (differential or cumulative) or full backup. All files are backed up if no previous backup was done. Differential incremental backups occur automatically according to schedule criteria. A complete restore requires the last full backup, the last cumulative incremental, and all differential incremental backups that occurred since the last full backup.

With those definitions defined, I would presume the standard backup schedule would be something like:

  • Monthly: Full
  • Weekend: Cumulative Incremental
  • Daily: Differential Incremental

 

Instead ours are set like this:

  • Monthly: Full
  • Weekend: Differential Incremental
  • Daily: Cumulative Incremental

 

Seems like an easy thing to fix, but the current numbers on alot of my jobs are indicative of the above file selection truly happening.  Look at this example of a client with native windows client backup policy.

The monthly full is labeled D here with 7GB and 60k files.  By definition, the Daily_Cuml labeled C is the changes since the full at 1GB and 484 files.  This all makes sense.  It continues to grow in both file number and size.  Now also by definition, I would expect the weekly_diff labeled "B" be smaller sinces its just the changes since the previous day.  But it isn't, its actually bigger in both number of files and size. To add to the confusion, the next daily_cuml "A" is SMALLER in both files and size even though it should be all the changes since "D".

????

I would expect them all to look more like this one:

 

Any insight as to whats going on here?  

7 REPLIES 7

Omar_Villa
Level 6
Employee

Mainly is what you want to do with the data when it changes, incremetal backups will backup the same file over and over if only changes one, but differentials will backup only what it changes but if the file is not modified again it will not take it, agaisnt incrementals that even if the file havent change ina full month you will be backing up the same data for the full month, this triggers the question if you can handle the load because eventualy it can acumulate a lot of data or make your incrementals near a full and expirience some performance issue, my recommendation is to run differential and fulls, in case of a restore you only need the full and the last differential.

 

regards.

MN_Pankaj
Level 4
Employee

You mention "client with native windows client backup policy"

 

You also provide two snapshots - but do not mention if they are from two different boxes, or even two different Windows boxes...

 

However, since you primary concern is in the first snapshot, we can explain that very nice and good. For a NBU Windows client, the default selection for doing backups is to use Windows OS's archive bit. See the selection "Perform incrementals based on archive bit" under the "Backup, Archive, and Restore client interface", under "File -> NetBackup Client Properties -> General tab"

 

For "Cumulative Incrementals", the archive bit is NOT cleared. So, subsequent "Cumulative Incrementals" can pick up all the files since last Full. For "Differential Incrementals", the archive bit is cleared AFTER that backup. So, the first "Differential Incremental" after a "Cumulative Incremental" would end up being a Cumulative itself, which is what you are seeing. And since the archive bit is cleared AFTER that "Differential Incremental", the next "Cumulative Incrementals" start again from ground zero.

 

In the second snapshot, where you think that things are working as you think they should, I bet that either that client box is Unix, or if Windows, has that selection for archive bit not set.

CypSteel
Level 2

Thanks for your replies, but NetBackup's definition of differential incrementals contradicts what your saying:

Differential Incremental Backup: Backs up the files that changed since the last successful incremental (differential or cumulative) or full backup. All files are backed up if no previous backup was done. Differential incremental backups occur automatically according to schedule criteria. A complete restore requires the last full backup, the last cumulative incremental, and all differential incremental backups that occurred since the last full backup.

I also checked the second computer and it did have the bit archive selection checked inside the netbackup client (windows).

MN_Pankaj
Level 4
Employee

From my understanding of the two snapshots, assuming both are windows (which it is indeed mentioned that they are):

 

1. First snapshot has archive bit selection - and the results are as expected

2. Second snapshot has archive bit selection NOT set - and the results are as expected

 

However, since you mention that the second snapshot does have archive bit selection, it is possible that that was done after the backups shown in that snapshot were taken...? Since you earlier mentioned that "I recently was moved to our backup and recovery" - it may be best to set the incremental selection same for both boxes, and let a fresh set of backups run, to confirm how the settings are and backups run. I am at a loss to understand how the second snapshot can happen with archive bit set...

 

Regarding the "NetBackup's definition of differential incrementals contradicts what your saying" - I would agree. I don't see how we can make that definition work for Differentials run after Cumulatives, with Windows Archive bit set. We can make that definition work without the Windows Archive bit set, since then things are totally under NBU Agent's control. Second, as you also earlier mentioned, the sequence of schedules is supposed to be Full-Differential-Cumulative and not Full-Cumulative-Differential.

MN_Pankaj
Level 4
Employee

On further thoughts and investigation, we do NOT support differential & cumulative at the same time, with Windows archive bit

 

See this boiler plate found in NetBackups Windows Administrator's Guide I (section Client Settings (Windows) properties - around page 98 (depending on your version of that guide))

 

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++

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.

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++

Mark_Solutions
Level 6
Partner Accredited Certified

As per the entry supplied above your policies really are not configured as they should be

I would suggest a complete review of your schedules for optimum data protection, especially in terms of data restoration - after all, that is why we back things up!

Many people do full backups every day to minimise the restore window

Those that do not have the backup window available on a daily basis to do full backups do weekly full backups and daily incremental (differential or cumulative) backups

It is all about recovery, so:

A Daily full needs just one days tapes to restore

A Weekly Full plus Daily Cunulative incrementals need just two sets of tapes to restore

A Weekly Full plus Daily Differential Incrementals need the weekly  plus every days tapes to restore

It is your choice but choose one of the above three according to any SLAs you may have relating to restore times

And consider also using TIR with Move Detection to make you restore really valid

Hope this helps

Yasuhisa_Ishika
Level 6
Partner Accredited Certified

Results of your backups can be explained clearly with Window's archvie bit.
You should set Incrementals based on Timestamp insted of Incrementals based on Archive bit to configure both cumu and diff incrementals.