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snapshot

Created: 03 Dec 2012 • Updated: 06 Dec 2012 | 10 comments
This issue has been solved. See solution.

I need to backup my D drive.When my backup runs,there is some activity on the D drive.

 

I am not using the disable snapshot method.I am using  snapshot should be created.

 

NBU 7.1.0.2

 

 

 

 when backup runs,Snapshor D' is created for volume D  which holds the changed blocks.

 

  1. Now Netbackup picks this D' or D?
  2. Snapshot is created when backup runs?
  3. snapshot is deleted when backup completes?

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Marianne's picture

Posting snapshot questions under multiple user ids will not attract different answers.

Please see https://www-secure.symantec.com/connect/forums/snapshots-0#comment-8038291 

and https://www-secure.symantec.com/connect/forums/snapshots-0#comment-8038291 

Supporting Storage Foundation and VCS on Unix and Windows as well as NetBackup on Unix and Windows
Handy NBU Links

Arun K's picture

I just want to know.I have only this id.

 

Please can anybody respond to this.

Arun K's picture

I have only one query regarding this.

  1. When backup runs,OS creates the entire volume snapshot of a drive.?
  2. D' is the snapshot of drive D.D' will be picked by NBU or D?

 

 

Arun K's picture

I just searched and find that NBU will pick up D'.

 

But can anybody please provide the other solutions.

VSS

Andy Welburn's picture

Snapshot usage

Selects how snapshots are made for the selected clients:
Individual drive snapshot
Specifies that the snapshot should be of an individual drive (default).Whenthis property
is enabled, snapshot creation and file backup are done sequentially on a per volume
basis. For example, assume that drives C and D are to be backed up.
If the Individual drive snapshot property is selected, NetBackup takes a snapshot of
drive C, backs it up, and discards the snapshot. It then takes a snapshot of drive D,
backs it up, and discards the snapshot.
Volume snapshots are enabled on only one drive at a time, depending on which drive
is to be backed up. This mode is useful when relationships do not have to be maintained
between files on the different drives.
Use this configuration if snapshot creation fails when all volumes for the backup are
snapshot at once when the Globaldrivesnapshot property is enabled. Individual drive
snapshot is enabled by default for all non-multistreamed backups by using the Windows
Open File Backup option.
Global drive snapshot
Specifies that the snapshot is of a global drive. All the volumes that require snapshots
for the backup job (or stream group for multistreamed backups) are taken at one time.
For example, assume that drives C and D are to be backed up.
In this situation, NetBackup takes a snapshot of C and D. Then NetBackup backs up
Cand backs up D.
NetBackup then discards the C and D snapshots.
This property maintains file consistency between files in different volumes. The backup
uses the same snapshot that is taken at a point in time for all volumes in the backup.
Note: The Individual drive snapshot property and the Global drive snapshot property
only apply to non-multistreamed backups that use Windows Open File Backup. All
multistreamed backup jobs share the same volumes snapshots for the volumes in the
multistreamed policy. The volume snapshots are taken in a global fashion.

 

....... from the Admin Guide!

Arun K's picture

Thanks Andy.

One more question:

When i run the full backup for the first time,the snapshot of D drive i.e D'  will have all the data of D?and NBU will pick this D'?

Arun K's picture

 

 

@Andy:The snapshot usage you have provided takes the snapshot of complete D drive? 

If i have 3 GB D drive ,then the snapshot will also be of 2 gb?

 

If it is so,i should have double the space on my D drive?

Andy Welburn's picture

You could say that a snapshot is a point in time 'copy'. Although the word 'copy' isn't quite correct!

Essentially it is a list or table of pointers to the data. So initially when you take a snapshot all it is is that list of pointers & so takes up very little space. As soon as data is changed, you could say that that pointer then changes to become the original data that it once refererenced, so over time as data changes the snapshot will consume more & more space until such time as all of the original data has changed in which case the snapshot will consume as much space as the original data did.

e.g. this is a *very basic* explanation of snapshots (& I apologise to anyone that takes offense from the way I have trivialised it!)

Imagine you have a volume that consists of three files:

file A = 1 Gb
file B = 2 Gb
file C = 3 Gb

You take a snapshot of said volume

snapshot = very little space (just pointers to the location of the original data)

Now you change file A such that:

file A = 4 Gb
file B = 2 Gb
file C = 3 Gb

snapshot = ~1Gb as File A has been completely changed

You now delete file B so:

file A = 4 Gb
file C = 3 Gb

snapshot = ~3Gb as File A has been completely changed & file B has been deleted.

You now delete file C:

file A = 4 Gb

snapshot = ~6 Gb (*everything* that was originally 'snapshotted' has been changed or deleted)

You could now delete file A which was changed to 4 Gb, but the size of the snapshot will not change to reflect this as *this* version of file A does not relate to when the original snapshot was taken.

 

I hope you manage to take something from this!

 

Arun K's picture

With Changed file here, you mean the active files on which writing is performed  duriing the backup on volume?

Andy Welburn's picture

*Any* file that is covered by the initial snapshot that changes in size has the potential to result in an increase in the space consumed by the snapshot.

SOLUTION