ReplicaSize calculation and significance RRS feed

  • Question

  • I am a long time user of DPM since 2010. I recently upgraded to DPM 2019 with MBS and disk storage utilization is harder to control. DPM likes to eat up storage with autogrow, so I was always able to keep it in check by manually assigning disk allocations.

    Now I am using DPM 2019 with MBS and I can't figure out how DPM determines the replicasize. I do know that the retention range affects it greatly. I also don't know how it affects the amount of data I can back up. DPM is showing me the amount used disk space which is inline with the Windows disk properties. So, do I need to worry about the replicasize or not? Will DPM become overprovisioned if the total replicasize exceeds the disk space even though I have not backed up that much data?

    In summary, I want to get the most out of the 7+ TB of backup space I have. We have less than 2TB of base data (VMs and files) to back up. I disabled AutoGrow on all Protection Groups and I have a script to increase the replicasize as needed.

    Side Q: I upgraded my original Win 2012 R2 / SQL 2012 / DPM 2012 server over the years to Win 2019 / SQL 2016 / DPM 2019. Should I just rebuild it from scratch?

    Friday, June 7, 2019 3:54 PM

All replies

  • Hello,

    With Modern Backup Storage (MBS) that ReFS, DPM can now improve the storage utilization.

    You shouldn't need to worry about the replica size really, DPM won't overprovision anything, it will give an error or warn if there insufficient space available.

    I would recommend installing a fresh DPM 2019 and start from scratch, also if you're worried about disk space, you might consider using data deduplication.

    More information over here: Deduplicate DPM storage

    I have also made a script that calculates the DPM replica and recovery point disk usage, you'll find it over here:

    Get DPM Replica and Recovery Point Disk Usage

    and on GitHub you can see some examples:

    Best regards,

    Blog: LinkedIn:

    Friday, June 7, 2019 5:06 PM
  • Thanks, I ran your script, similar to one I already had. Any insight on how the ReplicaSize, ReplicaUsedSpace and ShadowCopyUsedSpace values corelate to one another?

    Everything seems to be working OK on the server. Just not sure if a rebuild is worth it.

    Here's my concern, even though today I don't have a large amount of data to back up, I might later.

    From DPM
    Used space: 1,677.82 GB
    Unused space: 5,703.98 GB
    * This is OK and looks accurate for the data I backed up

    My concern is that the total of all replica sizes is about 3485 GB (added up all replica sizes)

    And the Disk Utilization Report shows 3918 GB Disk Used!

    Friday, June 7, 2019 5:31 PM
  • DPM will by default reserve space to protect the whole volume so as you protect more data the replica does not need to be grow.

    DPM allocates some extra space by default, here's a good old documentation on how the space allocation works for protection groups:

    Allocating Space for Protection Groups

    Blog: LinkedIn:

    Friday, June 7, 2019 5:53 PM
  • Thanks, but I tried using a the formulas for one of the VMs I backed up, but they don't align with DPM 2019 with MBS.

    Our VMs don't change much and we don't have a huge amount of changes or additions to our file server. So, I don't need large replica sizes.

    All I really need to know is if the total size of all replicas will prevent me from adding backup targets, even if I have plenty of free disk space to use for backups? I believe I saw a post where a user had this happen on DPM 2016, but I can't find it now.

    I don't like it, but I know how to fake out DPM into creating smaller replicas. I modify the PG and change the retention days to 1. Then I modify it again and add the target I want to back up. Then I modify it a third time to restore the original number of retention days. Stupid that MS makes you do this, but it works. I also disable AutoGrow for all PGs and I will use a script to increase the ReplicaSize as needed.

    Friday, June 7, 2019 6:38 PM
  • Yes these formulas were most likely changed for DPM 2016 and DPM 2019.

    All I really need to know is if the total size of all replicas will prevent me from adding backup targets, even if I have plenty of free disk space to use for backups?

    No as far as I know this should not prevent you from adding backup targets.

    Blog: LinkedIn:

    • Proposed as answer by Leon Laude Tuesday, June 11, 2019 10:56 PM
    Friday, June 7, 2019 10:07 PM