Disk space issues

Duc, Pham Phu 20 Reputation points

STTMailboxCapacity on DPM (GB)Number total recovery points on DPMPhysical capacity on the server (GB)1E19DB018.288,7912.630,002E19DB021.000,781679,003E19DB031.742,521787,004E19DB045.092,041766,005E19DB058.386,672750,006E19DB061.590,851886,00Why is there such a large difference between the physical capacity on the server and the capacity recorded on DPM?

Moved from: System Center Operation Manager

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AI answer

The large difference between the physical capacity on the server and the capacity recorded on DPM can be attributed to several factors:

  1. Data Retention Policies: DPM maintains multiple recovery points for data protection, and the total number of recovery points can significantly affect the reported capacity. If the retention policy is set to keep many recovery points, it can lead to a higher recorded capacity in DPM compared to the actual physical space used.
  2. Database Size: The size of the DPM database (DPMDB) can grow over time due to the accumulation of metadata and recovery point information. If the DPM database is bloated, it may not accurately reflect the physical capacity used on the server.
  3. Disk Usage and Fragmentation: The physical capacity may also be affected by how the disks are configured and utilized. If there is fragmentation or inefficient disk usage, the physical capacity may appear larger than what is recorded in DPM.
  4. Configuration Differences: Differences in how DPM calculates used space versus how the operating system reports physical disk space can also contribute to discrepancies. DPM may have specific configurations that affect its reporting.

To address these issues, consider reviewing the DPM database size, checking the retention policies, and ensuring that the disk configurations are optimized for performance and capacity management.

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1 additional answer

  1. Chen Tran 10,800 Reputation points • Independent Advisor

    Hello Duc,

    Thank you for posting question on Microsoft Windows Forum!

    Based on your query for the reason of why there is such a large difference between the physical capacity on the server and the capacity recorded on DPM.

    Well! The plausible explanation to that is the large difference between the physical capacity on the server and the capacity recorded on DPM (Data Protection Manager) comes down to how each system measures and reports storage. For Physical capacity on the server (GB). This is the raw disk space available on the storage hardware (e.g., total size of the disks/volumes). Whereas, for Capacity recorded on DPM (GB). DPM does not measure raw disk space. Instead, it tracks the logical size of the protected data sources (like mailbox databases) and the recovery points it maintains.

    DPM uses a technology called Volume Shadow Copy Service (VSS) to create recovery points. Every time a change is made to the database, DPM does not just record the change; it allocates space in the storage pool to keep the old version of that data. If your Exchange databases have high churn (lots of emails arriving, being deleted, or moved), the "Physical Capacity" grows to accommodate the history of those changes.

    On the other hand, DPM often stores recovery points using block-level incremental backups. This means only changed blocks are stored after the initial replica. As a result, the logical mailbox size reported by DPM can be much smaller than the actual physical disk usage on the server, because DPM avoids duplicating unchanged data.

    In short, the server’s physical capacity is the total raw disk space, while DPM’s recorded capacity reflects only the logical mailbox data plus recovery points, optimized with compression and incremental storage. That is why DPM shows much smaller numbers compared to the server’s physical capacity.

    Hope the above information is helpful! If it is. Free feel to hit "Accepted" for benefitting others in community having the same query too.

    1. Duc, Pham Phu 20 Reputation points

      My question is why DPM shows the storage capacity being used on the disk as much larger than the physical capacity of the server.

    2. Chen Tran 10,800 Reputation points • Independent Advisor

      Hi Duc,

      Based on your clarified question. Well! The most significant factor might be the Number of Recovery Points. As the server only holds the "Live" data (the current state of the mailboxes). Whereas, DPM holds the "Live" data PLUS every change that has occurred since your oldest recovery point. If you have 8,791 recovery points, DPM is storing a massive chain of "snapshots." Even if the mailbox is only 8 GB today, if users have deleted or moved 5 GB of data every day for months, DPM is physically storing all those "ghost" versions of the data so you can restore back to a specific minute.

      On the other hand, as I mentioned previously. DPM uses the Volume Shadow Copy Service (VSS). When a block of data changes on the Exchange server, VSS must copy the original block to a "diff area" before the new data is written. This process creates a massive amount of metadata and "shadow" storage. With 8,791 recovery points, the metadata overhead alone required to track those pointers can reach into the hundreds of gigabytes.

      You can consult the following articles for more information regarding your concern.

      Hope the provided information is helpful! If it is. Free feel to hit "Accepted" for benefitting others in community having the same query too.

    3. Chen Tran 10,800 Reputation points • Independent Advisor

      Hi Duc,

      Hope you are doing well!

      May I know the latest status of your query?

      Hope the provided information is helpful! If it is. Free feel to hit "Accepted" for benefitting others in community having the same query too.

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