Dell DL1000 Appliance Deployment Guide

Your DL1000 protection process begins when a base image is transferred from a protected machine to the Core. In this phase, full copy of the machine is transported across the network under normal operation, followed by incremental snapshots forever. The DL1000 Agent for Windows uses Microsoft Volume Shadow copy Service (VSS) to freeze and quiesce application data to disk to capture a file-system-consistent and an application-consistent backup. When a snapshot is created, the VSS writer on the target server prevents content from being written to the disk. During the process of halting of writing content to disk, all disk I/O operations are queued and resume only after the snapshot is complete, while the operations in progress will be completed and all open files will be closed. The process of creating a shadow copy does not significantly affect the performance of the production system.

Your DL1000 uses Microsoft VSS because it has built-in support for all Windows internal technologies such as NTFS, Registry, Active Directory, to flush data to disk before the snapshot. Additionally, other enterprise applications, such as Microsoft Exchange and SQL, use VSS Writer plug-ins to get notified when a snapshot is being prepared and when they have to flush their used database pages to disk to bring the database to a consistent transactional state. The captured data is rapidly transferred and stored on the Core.