arcserve-KB : ASBU | UDP Integration || Arcseve backup lite integration job is writing more data than occupied space on all the source volumes together.

Last Update: 2018-03-22 13:07:45 UTC
Problem Description:
Lite integration job is writing more data than occupied space on all the source volumes together.
For example C and D volume together constitute 0,8TB occupied space, whereas the Lite Integration Job writes 1,1 TB on the Tape.

Environment Details:
ASBU 17.5
UDP 6.5 Update 1
Destination Non Dedup datastore
The datastore is on a CIFS share

UDP Plan Details:
Agent based backup plan
Backup server where UDP and ASBU is installed is a physical machine and it is the same server that is being backed up 

On the UDP agent source machine the occupied space is around 800 GB = 0.8 TB

Troubleshooting done:

1.Checked the UDP side Full backup estimated backup size and we observe that an estimated 740.66 GB is being backed up.

'Informationen','19.10.17 09:00:45','','','196','Sichern','Geschätzte Sicherungsdatengröße. Volume=D:, Größe=740,66 GB.'
'Informationen','19.10.17 09:00:45','','','196','Sichern','Sicherung des Volume D: wird gestartet...'
'Informationen','19.10.17 09:00:45','','','196','Sichern','Sicherung des Volume C: wurde erfolgreich abgeschlossen.'
'Informationen','19.10.17 09:00:45','','','196','Sichern','Vergangene Zeit. Volume=C:, Zeit=29 Min. 47 Sek..'
'Informationen','19.10.17 08:30:58','','','196','Sichern','Geschätzte Sicherungsdatengröße. Volume=C:, Größe=72,16 GB.'
'Informationen','19.10.17 08:30:58','','','196','Sichern','Sicherung des Volume C: wird gestartet...'

2.From ASBU activity log we observe that the ASBU is writing 1.10 TB of data to the tape.

ASBU activity log
Informationen                   MAIN3                                25.10.2017 02:55:58      2349                    Verarbeitete Daten insgesamt........... 1,10 TB
Informationen                    MAIN3                                25.10.2017 02:55:57      2348                    Vorgang Sichern erfolgreich (Knotenname = MAIN3.RATHAUS.ROEDENTAL.DE)
Informationen                    MAIN3                                25.10.2017 02:55:57      2349                    Durchschnittl. Durchsatz: 2,94 GB/min
Informationen                    MAIN3                                25.10.2017 02:55:57      2349                    Vergangene Zeit: 6h 22min 38s
Informationen                   MAIN3                                25.10.2017 02:55:57      2349                    1,10 TB auf Datenträger geschrieben.
Informationen                   MAIN3                                25.10.2017 02:55:57      2349                    0 Verzeichnis(se) 25 Datei(en) (1,10 TB) auf Datenträger gesichert.
Informationen                    MAIN3                                25.10.2017 02:55:57      2349                    1 Sitzung(en)
Informationen                    MAIN3                                25.10.2017 02:55:57      2349                    ** Zusammenfassung für MAIN3 **
Informationen                    MAIN3                                25.10.2017 02:55:52      2349                    Datenträgerkomprimierungsrate: 1.37
Informationen                    MAIN3                                25.10.2017 02:55:49      2349     3             25 Datei(en) 1.150.697,88 MB von Agenten gesendet mit 3.007,11 MB/min
Informationen                    MAIN3                                25.10.2017 02:55:49      2349     3             UDP/D2D-Sitzung gesichert: S0000000006 (UDP/D2D-Sitzung gesichert um: 2017-10-23 19:00:31).
Informationen                    MAIN3                                24.10.2017 20:33:11      2349     3             Sicherungssitzung 3 auf Datenträger 11.10.17 01:00
Informationen                    MAIN3                                24.10.2017 20:33:11      2349     3             Quellverzeichnis: UDP Agent RAW Session
Informationen                    MAIN3                                24.10.2017 20:33:11      2349     3             Quellrechner: UDP/D2D [main3].

3. Made a ASBU client Agent backup on the machine and it is backing up only 660 GB. 

Informationen                    MAIN3                                26.10.2017 06:36:20      2351                    Durchschnittl. Durchsatz: 1,09 GB/min
Informationen                    MAIN3                                26.10.2017 06:36:20      2351                    Vergangene Zeit: 10h 6min 10s
Informationen                   MAIN3                                26.10.2017 06:36:20      2351                    659,08 GB auf Datenträger geschrieben.
Informationen                   MAIN3                                26.10.2017 06:36:20      2351                    102.771 Verzeichnis(se) 797.723 Datei(en) (661,63 GB) auf Datenträger gesichert.
Informationen                   MAIN3                                26.10.2017 06:36:20      2351                    15 Sitzung(en)
Informationen                    MAIN3                                26.10.2017 06:36:20      2351                    ** Zusammenfassung für Master-Job **

The following is the explanation for the increase in size of the data being backed up/written to the tape.

Resolution and explanation:
To understand the problem, we need to understand UDP design for a RAW disk backup.
After a snapshot is taken, the disk is divided by blocks, where each block is 64KB.
The idx file is to record the block numbers after a division of a raw disk.
If a file that is backed up ended in block N, N will be marked as used blocks, which will be backed up in copy-to-tape job. A file may be ended at the beginning of a 64KB block. 
For example, only 1KB is used by a file in block N. Block N is still marked as a dirty block, and the tape-copy-job will copy the whole block although only 1KB is used.
So in 64KB block size and 1KB is used and the remaining 63KB is called as white space. 

Once we understand the above design, the following statics report for the blocks used and the NULL-blocks not used will make sense:

From the  Backup log (BMAIN0702.log)
2017-10-25 02:55:34.620  <TID:6996><MAIN3 2349:2348>  UnivSendNoBufferingDataD2D: No. of NULL Blocks: 22778837.
UnivSendNoBufferingDataD2D: No. of total   Blocks: 41181696.
UnivSendNoBufferingDataD2D: No. of used bytes: 1206049767424.

total space=41181696x64KB=2513 GB=2.25 TB
not used space =NULL Blocks(22778837)x64KB=1390 GB=1.2 TB
Actual used space = 0.8 TB  'reported by Windows'
Data written to tape = 1.10 TB
UDP copy-to-tape up data = (total space) - (not used space) = 2.25 TB - 1.2 TB = 1.05 TB
White space backed up =  (Backed up data) - (Actual used space) = 1.05 TB - 0.8 TB = 0.25 TB
*other data = (Data written to tape) - (UDP copy-to-tape up data) = 1.10 TB - 1.05 TB = 0.05TB

Data written to tape = (UDP copy-to-tape up data) + (other data)

(*other data is from the meta data, such as catalog, index file, and other internal files used by restore)
Even though the actual used space is 0.8 TB reported by Windows,  the number of bytes backed up in UDP copy-to-tape job is 1.05 TB. The other discrepancy came from the meta data, such as catalog, index file, and other internal files used by restore.

This works as per the UDP design
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