Granular Restore Technology (GRT) used with a Backup-to-Disk (B2D) device results in the disk or the reserved disk space being filled up with overwriteable image (IMG) folders before the oldest IMG media will be overwritten.

Problem

Granular Restore Technology (GRT) used with a Backup-to-Disk (B2D) device results in the disk or the reserved disk space being filled up with overwriteable image (IMG) folders before the oldest IMG media will be overwritten.

Solution

It is expected that a B2D device used in GRT backup operations will result in the disk or disk space reserve being filled up with IMG folders before the oldest overwriteable IMG folder will be recycled on that disk partition or volume where the Backup to Disk Device resides. Taking this design behavior into consideration Symantec recommends the following:
 
1. Upgrade to latest version of Backup Exec.

2. Establish B2D devices dedicated to GRT backup operations on one disk partition or
    volume, separate from non-GRT backup operations that reside on another disk partition or volume.

3. Avoid using the option to "Allocate the Maximum size for backup-to-disk file" for B2D
   devices dedicated for use in GRT backup operations.

4. Avoid using a "disk space reserve" for B2D devices used in GRT backup operations
   unless overwriteable IMG folders will be available.

5. Avoid filling up a drive that hosts a B2D device used in GRT backup operations unless
   overwriteable IMG folders will be available.

6. Avoid running an Inventory job on a B2D device that has IMG media with Backup Exec
   11.0 build 6235. It is important to note that this issue has been resolved with Backup
   Exec 12.0 build 1364 and later versions. 
    
    
Recommendation 2
  
Establish B2D devices dedicated to GRT backup operations on one disk partition or volume, separate from non-GRT backup operations.
 
Example:
 
B2D-Data and B2D-GRT are B2D devices displayed in figure 1.
 
All backup jobs of data eligible for GRT backup should use B2D-GRT as the backup device on one disk partition or volume.
 
All backup jobs of all other data should use B2D-Data as the backup device on a separate disk partition or volume.
 
 
Figure 1
 
  
  
When examining a traditional B2D device in Backup Exec the device will show the contents as is displayed below in figure 2. Notice there is a single media type.
 
 
Figure 2
  
 
 
When examining the actual directory contents for B2D-Data, Windows Explorer displays the contents as is displayed below in figure 3.
 
Figure 3
  
 
 
So there is a correlation between the contents as displayed in the B2D-Data device and the folder where the backup data resides.
  
When examining a B2D device used for GRT backup operations via Backup Exec the device will show the contents as is displayed below in figure 4. In a B2D device used for GRT backup operations there are B2D and IMG media types.
 
 
Figure 4
  
  
  When examining the actual directory contents for B2D-GRT, Windows Explorer displays the contents as is displayed below in figure 5.
 
Figure 5
 
 
 
 
 
So, again, there is a correlation between the contents as displayed in the B2D-GRT device and the folder where the backup data resides. It can also be seen that B2D media represents a B2D file and IMG media represents an IMG folder. 
 
If it is necessary to mix GRT and non-GRT backup data in a single backup job, the GRT data will be written to the IMG folder and the non-GRT data will be written to the backup-to-disk file. This practice will create two different media types in one B2D device; an IMG folder type and a backup-to-disk file type. The mixing of the media types is not a problem for Backup Exec but rather a problem for a backup administrator when attempting to predict the frequency at which the two different media types will be available for overwrite operations since it is possible and even likely that the two media types will have media expiration dates that do not coincide. This behavior could result in a backup job that mixes GRT and non-GRT data being able to write to a backup-to-disk file but not an IMG folder and vice versa with the outcome being a backup job that is queued with a status of "Ready; No idle devices are available". This scenario is the reason for the recommendation to maintain separate B2D devices for GRT and non-GRT backups that reside on separate disk partitions or volumes.
 
 
Recommendation 3
 
 
Avoid using the option to "Allocate the Maximum size for backup-to-disk file" for B2D devices dedicated for use in GRT backup operations; figure 6 displays this option.
 
Figure 6
 
 
  
  

 This option is typically referred to as pre-allocation and is available on the General tab of each B2D device but only affects the B2D media and not the IMG media. When pre-allocation is used in a GRT backup, the backup-to-disk file will be created, mounted and grown to the pre-allocation size.
 
For a GRT backup, Backup Exec will mount a B2D media file in the B2D device specified in the backup job. If no B2D media file exists Backup Exec will create a new one. But Backup Exec does not write any GRT backup data to the B2D media file during GRT backup. All data is written to the IMG folder.
  
This means that if the first recommendation of maintaining separate GRT and non-GRT B2D devices has been followed then use of pre-allocation for a GRT B2D device will result in a B2D media file that is grown to the pre-allocation size and never used to hold backup data (all backup data will reside in the IMG media). This means all the space occupied by the B2D media file is wasted space. 
 
 
Recommendation 4
  
Avoid using a "disk space reserve" for B2D devices used in GRT backup operations unless overwriteable IMG folders will be available. The disk space reserve is configured in the Advanced tab of each B2D device, figure 7.
 
Figure 7
 
 
 
 
 
It's important to distinguish the concept of a "disk space reserve" from the concept of "specifying how much space a B2D device can occupy". A disk space reserve tells Backup Exec how much "total free space" must be available on the volume where the B2D device resides at any give time. If the "total free space" of the volume falls below the prescribed "disk space reserve" threshold at any time for any reason, then job processing will be affected.
 
 
Example:
 
The D: volume has a 100 GB capacity.
 
There is a single B2D device located on D: with a disk space reserve of 30 GB.
 
If no other data resides on D: then the B2D device can grow up to 70 GB.
 
This can be illustrated with the following formula:
 
Capacity of 100 GB - disk space reserve of 30 GB = the maximum space the B2D device can occupy of 70 GB.
  
But if "other" data is copied to D: then the maximum space the B2D device can occupy is reduced by the size of the "other" data.
 
 
Example:
 
The D: volume has a 100 GB capacity.
 
There is a single B2D device located on D: with a disk space reserve of 30 GB.
 
The D: volume also contains a shared folder to which users can copy data which occupies 10 GB of disk space (this shared folder represents "other" data).
 
Now the B2D device can grow to only 60 GB.
 
This can be illustrated with the following formula:
 
Capacity of 100 GB - disk space reserve of 30 GB - shared folder of 10 GB = the maximum space the B2D device can occupy of 60 GB
 
 
So the disk space reserve tells Backup Exec how much free space must be available on the volume, not how much disk space the B2D device is allowed to occupy.
 

 Each B2D folder has its own disk space reserve setting so if more than one B2D device resides on a volume it is necessary to account for the space occupied by the additional B2D devices. In such a scenario it is best to calculate the "maximum space the B2D device can occupy" of each B2D device independently and consider the additional B2D devices as part of "other" data. So as the additional B2D devices grow, the "other" data will grow and affect the "maximum space the B2D device can occupy" of all other B2D devices on the same volume.
 
 
Example:
 
The D: volume has a 100 GB capacity.
 
There are two B2D devices: B2D-Data and B2D-GRT
 
B2D-Data has a disk space reserve of 15 GB and has backup data occupying 20 GB of disk space.
 
B2D-GRT has a disk space reserve of 10 GB and has backup data occupying 25 GB of disk space.
 
The D: volume also contains a shared folder to which users can copy data which occupies 10 GB of disk space (this shared folder represents "other" data).
 
 
We must now calculate the size to which each B2D device can occupy independent of the other. We first start with B2D-Data and use the formula already established in the previous examples.
 
Capacity of 100GB - disk space reserve of 15 GB - shared folder of 10 GB - B2D-GRT of 25 GB = the maximum space that B2D-Data can occupy of 50 GB.
  
We now calculate the formula for B2D-GRT using the same formula.
 
Capacity of 100GB - disk space reserve of 10 GB - shared folder of 10 GB - B2D-Data of 20 GB = the maximum space that B2D-GRT can occupy of 60 GB.
 
 
From the examples above it can be seen that:
 
As "other" data grows the "maximum space a B2D device can occupy" shrinks.
 
As "other" B2D devices on the same volume grow the "maximum space a B2D device can occupy" shrinks.
 
 
Recommendation 5

 
Avoid filling up a drive that hosts a B2D device used in GRT backup operations unless overwriteable IMG folders will be available.
 
If the drive hosting a B2D device becomes full...
 
-OR-
 
If a B2D device has a disk space reserve limit set and that limit has been met...
  
...then the B2D device will go into a low disk space condition as well.
 
Figure 8 below shows a B2D device in a low disk space condition for B2D device B2D-GRT1-K
 
 
Figure 8
  
 
 
When a GRT enabled backup job targets a B2D device that is in a low disk space condition the Backup Exec Job Monitor will display the job state as "Scheduled" and the job status as "Ready; No idle devices are available" as seen below in figure 9 and the GRT enabled backup operation will not continue past that point. 
  
Figure 9
  
  
 When this occurs manual intervention is required. A user will have to take one of the actions listed below in the section titled Reclaiming Disk Space for Backup Operations and then unpause the B2D device before a GRT backup operation can resume or start.
 

Recommendation 6

 
Avoid running an Inventory job on a B2D device that has IMG media.
  
When this occurs Backup Exec for Windows Servers 11.0.6235 will move the IMG media into the "Backup Exec and Windows NT Backup Media" media set and the overwrite protection will be set to "Infinite - Don't Allow Overwrite" which will prevent the IMG media from being overwritten. Please note that BKF media in the B2D device will also be moved into the "Backup Exec and Windows NT Backup Media" media set but the BKF media will be available for overwrite operations.  
 
Reclaiming Disk Space for Backup Operations

 
The following conditions will trigger a GRT backup operation to automatically reclaim space on a drive:
 
The drive containing the IMG media becomes full or the B2D disk space reserve has been met.
 
- AND -
 
IMG media has expired within the Media Set selected in the Backup Job.
 

 When both of these conditions are met, Backup Exec will determine what IMG media should be erased to free up disk space. This is done by determining the oldest IMG media available for overwrite operations. At this point Media Set rules are followed and applied to the IMG media. Backup Exec then removes the oldest expired IMG media from the disk. Once that operation completes, the backups continue.
 
 
If a Backup Job is submitted when the B2D device is in a "Low disk space" condition and there is no IMG media available for overwrite operations, then the job will sit in a "Ready; No idle devices are available" state until one of the steps listed below is implemented to provide adequate disk space.
 
 
1. Erase IMG and / or B2D media via the Devices Tab, as displayed in figure 10, to provide adequate disk space.
 
 
Figure 10
  
 
 
 
2.  Free up disk space on the drive by removing data via Windows Explorer. The intention of this directive is to recommend removing data that does not reside in a B2D device. Removing files that reside in a B2D device will result in Restore Selections being inaccurate; remove "other" data. Do not manually delete B2D data or IMG Files.
 
3.  Wait for IMG or B2D media to expire according to the Media Set rules.
 
4. Remove the "disk space reserve" setting for the B2D device for the duration of the current backup operation and then take appropriate actions once the backup has completed.
 
 
After one of the options above has been implemented, manually pause and then unpause the B2D device as seen below in figures 11 and 12.
 
 
Figure 11
 
 
 
Figure 12
 
 
 
 

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