Data Protection Manager: What is a 'Consistency Check' and what could cause it to fail?

Data Protection Manger 2007 relies almost completely on a Consistency Check completing; hereafter referred to as a CC. What is a CC? A CC is a method in which DPM determines that a protected dataset is consistent with the Replica data set.

A CC is broken into three parts:

• (LWC) Lightweight Check
• (HWC) Heavyweight Check
• Fix-up

A consistency check is started after the Initial replica is created; hereafter referred to as an IR. When the IR completes, if the data set has not changed, the set is marked as consistent. Well what happens if the data changes between the time that you start the IR creation and the time that it finishes? The data goes through a CC.

If the data has changed, DPM, via the agents and the Volume filter (DPMFLTR.sys), begins a comparison of the file metadata (file date, file time, etc...) If this does not match, it runs an algorithm against the files and compares the results of the IR and the Protected Data. If they are still different, we invoke a fix-up. The fix-up is a block by block comparison of the IR with the protected dataset.

“So, what do I do if my dataset becomes inconsistent?” you may be asking yourself. Here are a few things to look for:

• Do you have any kind of backup software running on the protected server?
  • If so, you may be experiencing an issue where the archive bits are being flipped on the Protected Data set and it is changing the file enough for DPM to constantly notify the administrator that the dataset has changed
• How is your antivirus software configured on the protected server?
  • Configure your antivirus to delete files, not quarantine them. If antivirus quarantines the files, normally the files are locked and DPM cannot verify that they have not changed resulting in an inconsistent dataset. If you MUST quarantine files, then exclude the folder the quarantine folder of the antivirus solution you are using.
• Are you protecting a server that is a Windows Storage Server or a server that has SIS (Single Instance Storage) enabled?
  • SIS keeps a single copy of duplicate files. Sometimes the links back to the original instance become corrupt. When this occurs, it may be necessary to move the file to a different location and then move the file back. This deletes and recreates the SIS link back to the original instance of the file.
    • Unsupported files with the following files system attributes that DPM will not protect are:
      • Encryption & Reparse
      • Encryption & SIS
      • Encryption & Case Sensitivity
      • Encryption & Sparse file
      • Case Sensitivity & SIS
      • Sparse & reparse
      • Compressed & SIS
• Are you experiencing true disk corruption?
  • This is a last resort and will then require a manual CC to be invoked on the Protection Group. Run a command-line CHKDSK from inside the junction point

C:\Program Files\Microsoft DPM\DPM\Volumes\DiffArea\W2K3DC2.contoso.com\Non Vss Datasource Writer\Computer\SystemState\SystemState\chkdsk.exe

Author: Walt Whitman
Support Engineer
Microsoft Enterprise Platforms Support