In part 2 of my backup basics snippets, I introduce you to the concept of “not throwing the baby out with the bath-water” and what this means in backup-terms is that you do not delete your last-good backups before you have secured your next backup.
It seems for many so tempting to just wrench the retention period down to 0 and obliterate what might be in some cases a situation where a non-zero retention is the only valid recovery plan from the previous backup failure.
The mitigation of this risk has a capacity consequence, which should be calculated at the time of system design. The mistake illustrated here is most frequently encountered on database systems where there is often insufficient space to back-up the database once it breaches 50% of it’s data LUN.
If the data set is expected to be up to s Gb and c cycles are required then the backup volume or device needs to have the capacity of at least (c * s)+s Gb in order to hold sufficient copies of a backup; preferably on cheaper, albeit slower storage.
Do not skimp on backup storage if you want your DBAs to love you, they hate application-based backup agents and will give their left sock for a flat-file on-disk backup any-day!
Most importantly – it will also improve your RTO and if archive logs are available it will improve your RPO too.
The thing is to think ahead and always provision at least (c * s) + s storage for the backup volume
Keep this golden rule and your backup solution should remain fit for purpose given the finite storage resource available to the production data itself.