Imported tape backup copies may fail recovery.
Tape imports, not being able to support random read/write of more advanced format media, require a 2 step import process that requires additional storage space. Additionally, tape media has low reliability and block read errors will commonly fail imports.
When using tape media for cold backup copies, Unitrends recommends the Archive Format be set to our classic format 1. This increases tape read reliability for file level backups, allows for granular recovery of files from file backups from tape without full backup import (VM and Image and Database backups will still require full import), and eliminates the swap space needed to convert archive format 2 back to a readable backup which reduces free space needs for tape import dramatically.
To change to archive format 1 for all future cold copies created, access the appliance general configuration options from the Advanced tab when editing your appliance via the configure page. Search for the [Archive] ArchiveFormat value and change it to 1 from the default of 3. SZee the example below
Even with Archive format one, unless recovering granular files from file level agent backups, you will still require sufficient space in your appliance for up to 1X the full size of the original archive. If using Archive mode 2 or 3, you will require up to 2X the original size of the archive even for file recovery. If granular recovery from tape media of individual files is expected to be needed frequently, file level agent backups may be recommended over image or VM backups.
If insufficient space is not available prior to the import, the appliance will attempt to purge available backups that are not subject to a legal hold or LTDM retention policies. If insufficient backups are available to delete, or, deletion time is extended and space cannot be freed as fast as data is imported from tape, the import may fail.
Note: The appliance will continue to purge requested backups as able for backups already marked for deletion. This may result in an import that fails for insufficient free space but when later checked enough free space is available because these operations continued to run after the failure. Backup deletion is not a real time process can can take hours and in some cases days to remove all unreferenced hash blocks.
To eliminate double space requirements.
Archive file format 2 (represented as format 2 or 3 where format 3 leverages advanced database caching to increase the performance of the archive in some scenarios) leverages SIS blob objects for archive performance and storage efficiency. These are not deduplicated archives, however, they leverage some of our deduplication technology for efficiency. These files cannot be natively read without the support of random read/write capabilities of spinning disks or network shares. Tape lacks this technology. This forces all Archive format 2 backups from tape to require a 2-step import. First, the entire archive must be imported, then, it is converted to a readable local format. This requires up to 2X the space of a standard archive import. It also requires 100% of tape blocks to be bale to be successfully read for the entire backup even if the intent is to granularly recover a single file.