Source:SEP sesam Volume Shadow Copy Service (VSS) for Windows
Overview
From SEP sesam client version 4.0, every file system – Path backup of a Windows client has the option to backup with VSS enabled by default. For details on activating/deactivating VSS, see Activating/deactivating VSS-based backup. For details on excluding only specific VSS writers, see Manually excluding a VSS writer from backup.
About VSS
Microsoft Volume Shadow Copy Service (VSS) is a Windows service for backing up running applications. VSS coordinates with other VSS-aware applications and services, and creates a shadow copy or snapshot of data for backup purposes. VSS uses a copy-on-write snapshot, allocating a small temporary storage space for it. This does not occupy a lot of space because a snapshot contains only the data that has changed since the snapshot started. Once the snapshot is completed, the temporary storage space is freed up again. If there are any problem shadow copies remaining and occupying your disk space, check Microsoft tools Diskshadow and VSSAdmin to manage and delete shadow copies.
VSS architecture
VSS architecture includes the following objects and services:
- Provider: An operating system object that manages running volumes and create the shadow copies of them on demand as well as coordinates all elements. A VSS Provider is included in Windows installation.
- Requester: Typically, a VSS-aware backup application (in our case SEP sesam) that sends a snapshot request to the provider. It also communicates with writers to gather system information and to signal writers to prepare their data for backup.
- Writers: Services that prepare applications for snapshot creation and backup. They ensure that that their data is quiescent and in a consistent state. Once the snapshot is created, they let the applications resume.
Requirements
- VSS is provided on the Windows operating system versions beginning with Windows XP.
- Even though Windows has a limit up to 512 shadow copies per volume, a maximum of 64 shadow copies can be maintained. If the restricted total amount of created volumes is exceeded, VSS backup will fail. Note that the total amount of snapshots also includes snapshots that might be created with another application/for another purpose.
- Ensure there is enough disk space available for shadow copy. Microsoft article Troubleshoot VSS issues provides the following information: "For volumes less than 500 megabytes, the minimum is 50 megabytes of free space. For volumes more than 500 megabytes, the minimum is 320 megabytes of free space. It is recommended that least 1 gigabyte of free disk space on each volume if the volume size is more than 1 gigabyte."
SEP sesam backup with VSS
SEP sesam backup with VSS supports copy, full, differential, and incremental backups of file system only, therefore the option Backup with VSS should only be used with the backup type Path. All other backup types, for example System state, use the required VSS writer by default.
When performing VSS backup, SEP sesam as a requester requests a backup of the file system data specified in the backup task. VSS writers communicate with running applications and ensure that data is set to a consistent state and to stay consistent during the shadow copy creation. SEP sesam backs up the selected data immediately after VSS takes a snapshot of the selected data. Once the backup is completed, VSS instructs running applications to resume normal operation. File system data on the save set is stored with original location, e.g., C:\. This enables standard restore of data backed up with VSS. For details, see Standard Restore Procedure.
| ATTENTION |
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Ensure that the Microsoft AutoUpdate is disabled during backup with VSS. If the Microsoft AutoUpdate is running while backup with VSS is in progress, it might cause the backup job to fail with WIN32 API error: 21 – The Device is not ready. |
Activating/deactivating VSS-based backup
In the Main Selection -> Tasks -> By clients, select your Windows client and then click the backup task for which you want to change properties or click New backup task if you are creating a new task. After setting the task properties, enable or disable the option Backup with VSS. By default, VSS backup is enabled.
Backup with VSS activates all of the available VSS writers. If you want to exclude a specific VSS writer from backup, proceed as described in Manually excluding a VSS writer from backup.
Manually excluding a VSS writer from backup
Application specific VSS writers are used to coordinate and prepare application data for snapshot creation while it can still be in use. The following Windows software and services support VSS: Hyper-V, SQL Server, Exchange Server, SharePoint, Virtual Server, Active Directory, DHCP, WMI. You can exclude a specific writer from backup, if it is not needed for your current backup task (e.g., exclude a Hyper-V writer because you have another task dedicated for backing up a Hyper-V system).
You can exclude one or more VSS writers in the same way as you exclude data from backup.
1. In the Main Selection -> Tasks -> By clients, select your Windows client and then click the backup task for which you want to change properties or click New backup task if you are creating a new task. The backup task properties window appears.
2. Make sure that the option Backup with VSS is enabled. Then click the browse button next to the fields Source and Exclude list. Client file view is displayed.
3. Click the expand/collapse sign next to the VSS writers and select the writer(s) you want to exclude from backup. The excluded writers are listed in the Excluded field at the bottom. Clik OK to confirm.
VSS backup with SEP sesam version prior to 4.0
If you are running a SEP sesam client version older than 4.0, you can activate backup with VSS in the task properties under the tab Options 1.
1. In the Main Selection -> Tasks -> By clients, select your Windows client and then click the backup task for which you want to change properties or click New backup task if you are creating a new task. The backup task properties window appears.
2. Click the tab Options 1. In the field Save options, add option -o vss. The task source and other properties remain unchanged. Click OK to confirm.
