Monday , November 30 2015

What is loose Truncation in Exchange 2013 Sp1 DAG (Database Availability Group)?


Whats is Called Loose Truncation ? in Exchange 2013 Sp1

Lets make this simple ,

Normally if one Database copy goes offline in one of the DAG Members, Logs are not Truncated in all the databases copies , Which waits for the other failed copy to come back , so that other copies can help the failed copy to re sync the logs

But this situation doesn’t help admins all the time , Lets say I have a four node DAG , if I have one failed copy – logs stops truncating  . Disks get filled up , Which stresses the admins to remove the copy and reseed later

Exchange 2013 Sp1 introduces a new feature called loose truncation  – To avoid this situation

Loose Truncation is an optional feature in Exchange 2013 DAG – if loose truncation  is enabled ,  Where database copies will check their own disk space , if disk space gets low , All the databases copies will truncate logs independently

Now when the failed copies comes back – It cannot re sync as logs have been deleted , Two options to overcome or fix the failed copy  – Enable Auto reseed or Update the database manually

How To Enable Loose Truncation


You need to add the below registries on Every DAG member

There are three registry values you can configure


Step1 –

Start – Run – Regedit


Create a DWORD value




Below BackupInformation – Create Below DWORD values


LooseTruncation_MinCopiesToProtect – (Value 0 Is default – Disable Loose Truncation)

This key is used to enable loose truncation. It represents the number of passive copies to protect from loose truncation on the active copy of a database


LooseTruncation_MinDiskFreeSpaceThresholdInMB (200GB Is default – Free disk space Goes below default value – Loose Truncation is initated)

Available disk space (in MB) threshold for triggering loose truncation


LooseTruncation_MinLogsToProtect – (Default Values – 100,000 for passive database copies and 10,000 for active database copies)

The minimum number of log files to retain on healthy copies whose logs are being truncated

About Satheshwaran Manoharan

Microsoft Exchange Server MVP , Publisher of Supporting/Deploying/Designing Microsoft Exchange for some years. Extensive experience on Microsoft Technologies.

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