The backup infrastructure comprises the following components:
•One or more source hosts with associated datastores
•One or more backup proxy servers
The source host and the repository produce two terminal points between which VM data is moved. Backup data is collected, transformed and transferred with the help of Veeam transport services. Veeam Backup & Replication uses a two-service architecture — source-side transport service interacts with the source host, and target-side transport service interacts with the repository. These two services communicate with each other and maintain a stable connection. All backup infrastructure components engaged for the job make up a data pipe. VM data is moved over this data pipe block by block — processing of a single VM includes multiple processing cycles.
When a new backup session is started, the target-side transport service obtains job instructions and communicates with the source-side transport service to begin data collection.
1.The source-side transport service accesses a VM image and copies VM data using one of VMware transport modes, as prescribed by the proxy server settings. While copying, the source-side transport service performs additional processing — it consolidates the content of virtual disks by filtering out overlapping snapshot blocks, zero-data blocks and blocks of swap files. During incremental job runs, the transport service retrieves only those data blocks that have changed since the previous job run. Copied blocks of data are compressed and moved from the source-side transport service to the target-side transport service.
2.The target-side transport service deduplicates similar blocks of data and writes the result to the backup file in the backup repository.
As the backup job is running, the data blocks are written to the backup file on the file system of backup repository that you have selected as a backup target. Veeam Backup & Replication creates a full backup file (VBK) during the first run of a backup job. During every subsequent job run, it copies changes that were made to the VM since the last backup, whether full or incremental. Depending on the backup method you select, Veeam Backup & Replication handles incremental changes differently:
•If you use the incremental backup mode, Veeam Backup & Replication saves incremental changes to an incremental file (VIB) in addition to a full backup file (VBK) on the backup repository.
•If you use the reversed incremental backup mode, Veeam Backup & Replication injects copied changes to the full backup file, and saves replaced blocks of data as a reversed increment file (VRB) in addition to the full backup file (VBK) on the backup repository.
To review backup methods in detail, you can refer to the How It Works: Backup Methods section of this document, to Veeam Veeam Backup & Replication User Guide, and to online training video at http://www.veeam.com/backup-replication-university.html.
Also, in addition to backup files, Veeam Backup & Replication creates a backup metadata file (VBM) that contains information on the backup job, VMs in the backup, number and structure of backup files, restore points and so on. This metadata file facilitates import of backups and mapping of backup jobs to existing backups.