The V2.1 System State (using WBAdmin) plug-in produced very large patches, resulting in large backups and increased Storage Platform space requirements.
The V2.3 System State (using WSB) plug-in overcomes this problem backing up the individual System State files instead of a single VHD, resulting in:
The System State plug-in will automatically be upgraded from V2.1 to V2.3 if Backup Client auto-updates are enabled on the Storage Platform.
Both versions of the System State plug-in use Windows Server Backup (WSB) from Microsoft to perform the critical work. This process places most of the System State data in a single VHD file of around 8-12 GB in size. The V2.1 plug-in simply tried to patch this VHD file, but due to the way the data was stored in the VHD, the patch was very inefficient.
V2.3 of the System State plug-in overcomes this problem by splitting the VHD file into individual files before starting the backup process. This allows the Backup Client to
During the restore process, the individual (split) files are restored and then combined to recreate the original VHD file before WSB is again used to perform the System State restore.
The V2.3 System State plug-in will request that WSB do an incremental System State backup which is much faster and patches even better than a clean System State backup. In effect, it re-uses the previous VHD file instead of creating a brand new one. According to Microsoft, this can only be done when a number of (unpredictable) conditions are met (for example not too much disk activity since the last WSB backup). If an incremental backup is not possible, a clean VHD file will be created, leaving the original VHD file temporarily on the disk. Therefore, temporary space is required for up to two System State backups instead of only one.
Even if WSB manages to do an incremental backup, the System State plug-in still splits out the VHD into individual files, thereby requiring the extra space regardless. However, these two processes do not happen at the same time and the extra files are deleted when the backup completes. Therefore, the total extra space requirement (compared to the V2.1 System State plug-in) is the size of one extra VHD file.