More about the SBS 2011 standard and essentials backup engine

I’m posting this as a FYI


http://social.microsoft.com/Forums/en-US/partnerwinserverebs/thread/0022ed92-b0a5-461b-82dc-f4a29d93550d


From your description, I understand that:

You configured two 500GB external drivers for server backup. After 105
days of daily backups, it now reports low space warning. You wonder how
the backup space is automatically managed, and how to properly deal with
the low space warning.

If there is any misunderstanding, feel free to let me know.

First, sorry for the delay due to weekend. I realize that you posted the
question on public SBS forum. Please kindly understand that the public
forums are NOT monitored by us. For your information, the partner forum
is labeled as (Partner) such as *Windows Server (Partner) Forums*.

Ira, it is actually frequently asked questions – how disk usage is
automatically managed by Windows Server Backup? Why sometimes backup
would fail with target out of disk space in spite of automatic disk
usage management feature in Windows Server Backup?

The storage team has an official blog to address the inquiries:

Windows Server Backup automatic disk usage management

http://blogs.technet.com/b/filecab/archive/2011/03/14/windows-server-backup-automatic-disk-usage-management.aspx

The blog explicitly answers the following questions:

Q1. What is Automatic disk usage management feature in Windows Server
Backup?

Q2. How does the auto-delete functionality of Windows Server Backup works?

Q3. What are the criteria on which this feature works?

Q4. Why does backup fail with target out of disk space in spite of
automatic disk usage management feature in Windows Server Backup?

To summarize and address your questions:

1. Windows Server backup (WSB) does automatically manage the disk usage.
It can automatically reuse the space occupied by older backups when
creating new backups.

The Automatic Disk usage management feature comes into play when WSB
detects that the backup target does not have enough space to accommodate
the backup while backup is in progress. The way WSB creates space for
new backup is by shrinking the storage space allocated for snapshots
(called diff area). As a result, one or more older snapshots (and hence
backup versions corresponding to those snapshots) occupying the diff
area that got shrunk get deleted. Before shrinking diff area, WSB
determines whether shrinking the diff area can free up the requisite
space so the backup can happen. If enough free space can get created,
WSB goes ahead with the shrinking and continues with the backup.*WSB
will not shrink the diff area to less than 1/8 of Target volume size as
we do not want to lose all past backups just to accommodate this one.
This is why sometimes backup fail with target out of disk space in spite
of automatic disk usage management feature in Windows Server Backup.*

**

Note: Space used by a System state backup is not automatically managed.
See the section “*How to Delete System State Backups*” section of the
following article for managing system state backups.

Backup Version and Space Management in Windows Server Backup

http://blogs.technet.com/filecab/archive/2009/06/22/backup-version-and-space-management-in-windows-server-backup.aspx


For example, you can keep the latest N versions of system state backup
on a backup storage location via command:

*Wbadmin delete systemstatebackup -keepversions:N*

**

2. As explain by the official blog, if you receive the low space
warning, it means WSB has reached the state where the space required to
complete the new backup causes the snapshot storage space to become less
than 1/8 of the target size. In this case, you can manually delete the
old backups created by WSB per this article:

http://blogs.technet.com/filecab/archive/2009/06/22/backup-version-and-space-management-in-windows-server-backup.aspx


For example, you can delete the oldest shadow copy on the backup storage
location via command:

Diskshadow.exe

Delete shadows OLDEST \\?\Volume{GUID}

3. Only the number of System state backup can be configured via command
*Wbadmin delete systemstatebackup -keepversions:N*

**

It is because the space of system state backup is not automatically
managed. For fully server backup or volume backup, WSB uses VSS to
maintain backup version and automatically manage disk usage via the
Automatic Disk usage management feature as explained before.

Hope the information helps.

————————————————————————
Best regards,

*Tony Ma
*Partner Online Technical Community

One Thought on “More about the SBS 2011 standard and essentials backup engine

  1. Thank you !

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