Differential backup Size Compared to sum of T-Log Backup Sizes

  • If I do a full backup on a Sunday and a diff backup on Monday at 11pm and do t-log backups every 15mins, would I expect the size of tMonday's diff backup to be roughly equal to the sum of all the t-log backup sizes done throughout Monday?

  • not a necessity, depending on the nature of your transactions.

    Transactionlog: value before/after transaction. If committed you could count it as changed

    Diff=changed data since full (rolled back=not changed)

  • I would say, most definitely not...

    The transaction log will contain a record of all transactions that have occurred - and also contains the information needed to rollback a transaction and/or roll forward that transaction.

    A differential backup only backs up data that has been marked as changed since the last full backup has been performed.

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    Managing Transaction Logs

  • No they cann't be same as the data stored in a Differential backup includes only the transaction log files up to the current checkpoint and transaction log contains all the committed and uncommitted transactions.

    -MJ
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