Projecting disk usage based on allocation formulas RRS feed

  • Question

  • I'm having trouble getting the calculations from technet to match up with actual protection groups I'm building and it's creating some concern about our ability to project disk consumption.  The question is, how do I accurately project disk consumption as we add new protection groups in DPM 2010 using the forumlas provided in technet.

    I have two protections I'm working with right now that I'm trying to run the math on as we prepare to protect a critical system this weekend.  Protection Group A is a 437MB folder that we are protecting for 120 days.  Protection Group B is a 132GB folder that we are protecting for 14 days.  So based on my math looks like the following is what would be consumed based on replica and recovery point combined.

    Protection Group A (437MB folder for 120 days)

    [(437MB * 3) / 2] + [(437MB*120*2 / 100) + 1600MB] = (655.5MB + 2648.8) = 3304.3MB or ~3.23GB

    In DPM, I am currently seeing 2.73GB allocated to this protection group.  This is a new protection group that I just created today.  That seems closer to just the recovery point volume size but even then is still a bit off.  Regardless, at least actual allocated space is somewhat close to what I would project based on the formulas provided.

    Protection Group B (132GB folder for 14 days)

    [(132GB * 3) / 2] + [(132GB*14 * 2 / 100) + 1600MB] = (198GB + 36.96GB + 1.56GB) = ~236.52GB

    In DPM, I am currently seeing 1,566GB allocated to this protection group.  This is a protection group that's been running for a few weeks now.  But it's about 7x what the calculation would come out to be.

    So neither of these protection groups really reflect an allocated space that matches the formulas given in technet.  I'm at a bit of a loss on how to accurately project consumption of disk space with DPM if I can't get these formulas to match what I'm seeing.  Any help or insight would be appreciated.  I'm sure I'm missing something but am just getting into DPM so I haven't caught what it is.

    Thursday, November 17, 2011 9:30 PM

All replies

  • Are you still having this issue?
    Thanks, Wilson Souza - MSFT This posting is provided "AS IS" with no warranties, and confers no rights
    Tuesday, January 17, 2012 5:22 AM
  • When protection File data, DPM is only able to go to 64 disk based recovery points. So for protection group A if you put in 64 recovery points you'll get about 2814MB or roughly 2.74GB (give or take). Which is similar to that allocated in DPM.

    As for the difference with what protection group B and DPM has actually done is the difficulty in projecting the rate of change of data in any environment. The figures Microsoft have provided are those which show "how DPM calculates the default allocations". This is not indicative of what the rate of change is going to be in your environment but a guess from Microsoft as to how much you should allocate.

    What is really happening here is that the recovery point volume is tracking the block changes for the file data that you are backing up. So if someone goes and deletes xGB of data blocks in one day, then the RP volume will reflect that space required for the retention period, in protection group B's case 14 days. While this is good for tracking the changed blocks of files rather than the entire file if part of that file is modified it does have some drawbacks. Also because the DPM backup to disk process uses block level tracking - if someone regularly runs a defrag on the volume that contains the data you are protecting then DPM will see the block map change and transfer those changed blocks to the recovery point volume.

    So is Protection Group B a volume that has a lot of changes to it (large files being added, moved or removed regularly) or a process like defrag running? And is the automatically grow DPM volumes configured for that protection group. Have a look at the size of the RP volume, what is allocated and what is used to give you and idea of how DPM is using that space.

    Also look at the monitoring tab on protection group B and look at the completed backup jobs (filter if necessary) so see what the daily transfer to the RP volume is to give you an idea of the daily block change data size.

    Hope this is helpful.

    Friday, January 20, 2012 3:35 AM