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Replication Workflow

4 Aug 2014 by anth

Unlike storage-based replication solutions which use block-based replication EVnearSync uses object based replication to provide a safe, reliable and fast replication process which is integrated into the DNA of Enterprise Vault. This allows a primary and secondary copy of Enterprise Vault to be maintained in different locations without needing to match storage platforms.

It also protects Enterprise Vault installations from replication of corrupt storage blocks which otherwise could destroy a secondary copy and make failover impossible during an outage.

EVnearSync makes use of Enterprise Vault’s “safety copy” feature to provide a completely supported mechanism where replication is integrated in the archiving workflow.

A typical Archiving Workflow with EVnearSync in place to replicate archived data would look like:

ns-workflow

The steps are as follows

  1. During the archiving schedule Enterprise Vault connects to the user’s mailbox on the Exchange Server using the MAPI protocol and, dependent on policy (e.g. older than 30 days), it copies the items which match the policy to the Enterprise Vault Server. The “original” items are still available on the Exchange Server but they now have the altered message class of IPM.Note.EnterpriseVault.Pending.Archive.
  2. The metadata of the copied item is inserted into the Enterprise Vault database (Vault Store DB, Fingerprint DB and folders in the directory DB)
  3. Depending on the Single instance (SIS) settings on the Vault Store Group hashes will be calculated on the items’s different parts (body, attachments etc) and the item will be split into different files. These proprietary Enterprise Vault files will be written into the open partition of the Vault Store
  4. The index for the item is created and stored on the file system.
  5. EVnearSync now gets triggered by Enterprise Vault. It reads the EV Databases to determine which files have been archived since the last query. It replicates each object (i.e. file by file – all the files within a single EV transaction) to the replication target in the second data center
  6. EVnearSync calculates SHA-256 or MD5 hashes to ensure the quality of the replication. Both source and replicated files will be hashed. If the hashes match the replication is known to be successful
  7. At this point EVnearSync provides feedback to EV that the item was successfully written and the archiving storage is now safe as there are two copies.
  8. Enterprise Vault deletes the original item from Exchange and replaces it with a shortcut

Steps 5 to 7 are additional steps carried out by EVnearSync. Because there are always two copies of the item at the same time (either in Exchange and in the archive storage – or in the archive storage and the replication target) it is impossible to have data loss. The original item in Exchange will only be deleted if the replication was successful.

This workflow produces an RPO of zero.