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Adding new DDB partition

  • 9 January 2023
  • 5 replies
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Userlevel 1
Badge +6

Hello,

Planning to add a new partiotion to an exiting DDB. I’ve went through the documention and have a doubt on the below.

The addtional 0.5MB of data will be added only to the magnetic disk the holds the DDB or will it be also added to the Disk library mount paths ?

 

“After running the Backup1, you add Partition2 and run Backup2 of the same 1 MB of data. After the second backup, 4 signatures of 128 KB size will be added to Partition2 (even though the same signatures exists in the original store) and for the other 4 signatures only the reference will be added in the original store (as the signatures already exists). The magnetic disk will have 1.5 MB of data (1 MB from the first Backup + 500 KB from Partition2 from Backup2).

On running data aging, if Backup1 is aged, then from the first partition the first 4 signatures will be aged and also 500 KB of data will be pruned from the magnetic disk.”

https://documentation.commvault.com/2022e/expert/12455_configuring_additional_partitions_for_deduplication_database.html

 

Thanks

 

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Best answer by Laurent 9 January 2023, 10:35

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Userlevel 6
Badge +15

Hello !

It will be added to the DDB ‘volume’.

In the documentation, ‘DDB’ is reffered to as the database entity (whole set of files that altogether are the deduplication database), while ‘magnetic disk’ is the storage/volume hosting the DDB.

Userlevel 1
Badge +6

Got it.

Thanks

Userlevel 3
Badge +8

Hi, 

If you concern is disk filling in the DiskLibrary I can confirm that these lines in the same doc-section is correct…

“New baseline for the DDB store is started each time a new partition is added and some of the same signatures might be written to the new partition even though they exist in the DDB store.

The data is aged when there are no more references to the blocks left and then the data is pruned physically from the DDB as well as from the magnetic disk.”

….a new baseline is started and you will have extra diskfilling in the DiskLibrary according the the calculation described in the same doc-section. 

@TNO: Did you add a new partition? Did you also experienced the DiskLib getting extra filled due to the new baseline? 

Br,

Patrik

Badge +3

As per my understanding if you have 2 partitions of DDB and expand to 4 partitions you need 50% extra space in Disk Library. So if baseline is 100TB with 2 partitions and then after expanding to 4 partitons it would be 150TB. It’s baseline (after compression), so the overhead will be a little bit less but in general this operation utilized disk library in extreme way.

 

@TNO@Patrik can you confirm your experience after expanding DDB? Can you share your findings?

Userlevel 3
Badge +8

Hi Maciek, 

In our case we had 3 DDB-partitions and added one more. Before adding the 3rd partition we had a growth of ca 50TB per month, after adding the additional partition the growth was 150TB/month and continued to grow rapidly, so we had to lower the retention to not fill the DiskLib. 

As we had to lower the retention I cannot confirm that the documented estimations in baseline-growth are accurate. But I would expect that they are estimates, as always when calculating on dedup-data. 

 

So I can confirm that the increase in baseline data described in docs is indeed the DiskLib baseline.  

/Patrik

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