DLM will reclaim any backup set that is expired, with the exception that if all copies of a given backup set are expired, by default the last recovery chain will not be reclaimed, even if it is expired (this restriction can be disabled).
Excepting when using removable (RDX style) disk storage, these reclaims occur in the background on a regular cycle and are not triggered by the activity of backup jobs, however reclaims can only take place against backup sets held in online storage devices.

During normal activity where the disk storage remains online, older backup sets are reclaimed (deleted from the system) not long after they expire, and as such, by design there would be no expectation of being able to restore from online older expired sets.

If a customer is detaching the disk storage device from Backup Exec, with the intention of physically managing a longer retention by limiting access to the storage device, then as long as the disk storage is maintained as an offline device inside the storage configuration of Backup Exec then after 2 weeks of being offline for USB, local disk, SAN or NAS drives OR after 4 weeks of being offline for removable/RDX style cartridges, the device or cartridge in question will be marked as "Limited to Read Only" and will not allow reclaims when reconnected. Note: the 2 week/4 weeks timings are defaults and can be adjusted within the storage settings of Backup Exec.

If however the disk device is detached / made unavailable to the Backup Exec server and also deleted from inside the Backup Exec Console, OR moved to another Backup Exec server in a DR situation, then because that installation of Backup Exec is not managing the device in question as an offline device, reclaims can take place against any expired sets when the device is added into Backup Exec and Inventory (or in some cases Inventory and Catalog) operations are run.

As such situations that can cause this deletion of older backup sets are:

1. The device in question is not RDX and has been detached and deleted from Backup Exec. Enough time has passed for the backup sets in question to have passed their expiration date and then the device is attached to the original server  and configured as a 'new' disk storage device. An inventory (or inventory and catalog) is run
2. The device in question is not RDX. Enough time has passed for the backup sets in question to have passed their expiration date and then the device is attached to a different server (or a rebuilt version of the same server where the BEDB has not been recovered). An Inventory and catalog is run (or an inventory only if the catalog files were copied/recovered)
3. The backup set in question is already expired on an RDX cartidge and the cartridge is used in a different server (or a rebuilt version of original server without the original BEDB).  Inventory and catalog operations are run, however before a restore is attempted a new backup job writes data to the cartridge (which for RDX triggers the reclaim operation)

To avoid automatic reclaims in restore situations:

• Do not delete offline disk devices from Backup Exec where the backup sets still exist on the device in question and you intend to re-configure the device back onto the same Backup Exec server in the future (maintaining the device in an offline state not only lets Backup Exec mark the device as limited to read only after a set time period, but will also allow manual application of the same setting via the device properties whilst it is offline)
• If using removable storage/RDX devices, before inserting the cartridge,  slide the physical write protect tab (if present) across on the cartridge itself. This works in a similar way to the physical tape write protection tabs.
• For disk storage devices that cannot be directly set to write protected, before connecting and configuring the disk storage device, disable DLM using the information in https://www.veritas.com/docs/000021156   Note: Once you have access to the device in question inside of Backup Exec but with DLM disabled, inventory and catalog operations can be run safely and it is then possible to manually set new expiration dates on specific backup sets OR set the device with "Limit to Read Only" enabled, which will allow DLM activity to be re-enabled against other devices and/or sets

  DO NOT LEAVE DLM PERMANENTLY DISABLED - If DLM is left disabled then disk space issues will occur as further backup jobs run.

With the introduction of Data Lifecycle Management (DLM), Backup Exec will delete (reclaim) any expired backup sets from disk based storage. Administrators that may be storing disk based sets in disconnected/offline devices as longer term storage (or to use with a DR situation or a DR site) may experience automatic reclaims against the backup sets in question, when the disk storage is reconnected in order to perform a restore. As reclaim activities take place in the background this removal of older backup sets could impact the ability to restore.

This articles discusses the causes and provides a link containing information on how to disable DLM

ETrack: 3900980