Explanation
Why the waste happens and who it affects.
When a SQL Server backup policy is created, a daily full backup is the default, and HANA policies can be set up the same way. Each daily full is a complete copy of the database that is kept for the full retention period, so vault storage grows with database size multiplied by the number of retained days.
Point-in-time recovery comes from the log backups, not from the frequency of full backups, so a weekly full plus daily differential or incremental backups plus logs usually meets the same recovery point objective. Microsoft's HANA backup FAQ ranks daily full plus logs as the costliest policy and weekly full plus daily incremental as the least expensive, and Azure Advisor flags database workloads that could use differential or incremental backups. The tradeoff is restore time: a restore needs the full plus the differential, or the full plus every incremental since it, before logs are applied.
Billing model
The pricing dimensions that drive this cost.
Workload backup for SQL Server and SAP HANA in Azure VMs is billed as a protected instance fee plus the vault storage consumed by retained recovery points.
- Protected instance fee
- Monthly charge per protected database instance, tiered by the size of the backed-up data before compression
- Backup storage
- Billed per GB per month for all retained recovery points, at the rate of the vault's redundancy (LRS, ZRS or GRS)
- Full backup
- A complete copy of the database, retained until its own expiry and until every dependent log backup has expired
- Differential or incremental
- Stores only changes since the last full (differential) or last backup (incremental), so each retained copy is much smaller
How to detect
4 checks to find it in your estate.
- Review Azure Advisor for 'Use differential or incremental backup for database workloads' on Recovery Services vaults
- List backup policies of workload type SQL Server in Azure VM and SAP HANA in Azure VM whose full backup schedule is Daily (in the policy's subProtectionPolicy list, the entry with policyType Full and a Daily scheduleRunFrequency)
- Compare backup storage growth in the vault (Backup Reports or cost analysis for the vault) with the size of the protected databases; storage many times the database size with daily fulls points to this pattern
- Check whether SQL Backup Compression is enabled on SQL Server policies; it is off by default
How to fix
5 ways to remove the waste.
- Change SQL Server policies to a weekly full backup with daily differential backups and log backups at the required frequency; differential backups are only available when fulls are weekly
- For SAP HANA, move to weekly full plus daily incremental (lowest storage) or daily differential (faster restore) plus logs
- Before switching, review the policy change rules: changes apply retroactively, so earlier daily fulls not on the new full-backup day are marked for deletion but kept until the logs that depend on them expire
- Validate that the longer restore chain still meets the recovery time objective, since restores need the full plus differential or incremental copies before logs are applied
- Enable SQL Backup Compression in SQL Server policies where CPU headroom allows, to reduce the size of each backup sent to the vault
Documentation
Vendor references for pricing and configuration.