Log backups (transaction, archive, or logical logs) are not considered part of the backup cycle. Therefore, storage policy cycle retention parameters do not apply to them. However, log backups may be linked to data backup operations, which can affect their retention as follows:
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Log backups are linked to a full backup if they are run at the same time. This is regardless of whether the full backup included data only or data and logs. Such backups follow the standard data aging rules.
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If a full backup job is run on data and logs, then the next log backup will not be linked to this full backup job. These are unlinked log backups and by default, this will follow the unique data aging rules for log backups as follows:
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Logs that need to be copied to secondary copies will not be aged, both on the primary and non-primary source copies.
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Logs that exist only on one copy will be aged when they are older than the oldest data.
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When logs exist on multiple copies, the logs on the copy with the longest retention days will be retained with the data and will be aged after the oldest data. The log jobs on the remaining copies will be aged according to copy retention days without checking if the oldest data exists or not.
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Partial, disabled logs will be aged when they are older than the oldest data.
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If a full backup job is run on data, then the next log backup job will be linked to this full backup job. These are considered as linked or chained log backups and are not aged until the linked data is aged. In addition, these log backups will also follow the unique data aging rules for log backups.