Is Synthetic backup the same as Progressive Incremental?

I’m asked this quite a lot, so I thought I’d do a quick blog about it. There are several methods for backing up data, ranging from Full every day to Progressive Incremental. Here is a quick overview of the pros and cons:

full_every_day

Pros: Simple, easy to recover from a single image

Cons: Very wasteful of storage space

full_and_incs

Pros: Simple, easy to understand, much more efficient use of space than Full every day, faster backups

Cons: Repeated (typically weekly) fulls required as recovery becomes more complicated as days elapse from the initial full backup, due to making a recovery for each day.

full_and_diffs

Pros:  Only the full and the current daily backup are required for recovery

Cons: Less efficient use of space, increasingly slow backups as days elapse from full backup

synthetic_full

Pros: Only incremental backups are taken from client, therefore faster than full/inc

Cons: Heavy processing used at server to create the synthetic full and no extra space savings over full/inc

reverse_inc

Pros: Todays backup is always stored as a full, therefore fast, simple recovery

Cons: Various implementations on the market appear prone to corruption of the full and therefore require ad-hoc full backups. Full or synthetic full backups still required so no space savings over full/inc.

progressive_inc_forever

Pros: Only a single full ever required. Backups are fast and extremely space efficient. This is the Gold Standard.

Cons: Complex database structures required, poorly configured systems can require multiple media mounts for restores.

Progressive Incremental backups have been proven in ADSM/TSM/Spectrum Protect since the late 1980s, database performance with Protect is excellent and the objections of complexity that are sometimes brought up have been shown over several decades to be non-issues.

Some traditional full/inc based packages can re-point databases entries in the deduplication system to create new full backups, rather than relying upon traditional synthetic fulls. This means that a very fast synthetic full can be created, however the only implementations on the market require the use of the packages own built-in dedupe system and do not work on non-deduplicated backups. Any space efficiency is lost when moving data out to long term tape or external disk/object storage.

It appears that after some 28 years on the market Spectrum Protect is still the only package offering true Progressive Incremental Forever over it’s entire client range.