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"Refresh" data on secondary dpm server from tape? RRS feed

  • Question

  • We have a secondary dpm server (dpm2) which backs up the protected data on our primary dpm server (dpm1) every night.  There are a few jobs that have gotten out of sync, and running a consistency check takes far too long, and never completes.  Is it possible to take a tape backup from dpm1 over to the secondary site and have dpm2 update it's copy from the tape?

    If so, do I need to do anything special to create the tape backup for this, since dpm2 is technically backing up dpm1, not directly backing up the protected servers? 

    Monday, December 19, 2011 3:02 PM

Answers

  • Hi,

    If you have a tape drive on both DPM Servers, you can take a long term backup of the file data from the Primary DPM server, then ship the tape to the offsite location.  On the Secondary DPM Server, the tape will show as imported.   Re-catalog the tape then under the External tapes tree under the recovery tab, you can restore the data to the replica volume, exactly the same way as you would do it for a manual replica load.  Then start a new consistency check.

     

    <snip>
    Just to be clear, you're saying with dpm2010, bmr backups replicating to a secondary dpm server will always transfer the full system image, as opposed to just the actual data that changed on the original server.  Is that correct?   Will that be changing in dpm2012?  
    >snip<

    This is not a DPM problem, DPM is bringing over all the blocks that changed on the primary DPM server as a result of the Windows server backup overwriting the .VHD file(s) - DPM is working properly, so there is no change in DPM 2012.

     


    Regards, Mike J. [MSFT] This posting is provided "AS IS" with no warranties, and confers no rights.
    • Marked as answer by NeighborGeek Tuesday, December 27, 2011 6:25 PM
    Tuesday, December 27, 2011 6:14 PM
    Moderator

All replies

  • Hi,

    There is no way to avoid the consistency check. Even when re-seading the secondary dpm replica using tape data from the primary will still require the consistency check.

    It sounds like you have a combination of lots of data to check and a slow link and that is why the CC is talking so long.

     


    Regards, Mike J. [MSFT] This posting is provided "AS IS" with no warranties, and confers no rights.
    Friday, December 23, 2011 1:34 PM
    Moderator
  • Mike -- Under normal circumstances, a consistency check doesn't transfer the data in it's entirety over the network does it?  So if i could get the initial replica of the new data on dpm2, a consistency check of it should be able to succeed.  I know you can create an initial replica manually (i.e. from tape or external drive) when adding a new protection group, but I don't know how that works when backing up the replicas from the primary dpm server, as opposed to directly backing up the file server. 

    We have a 10Mb connection between the WAN sites, but we recently combined data from 2 file servers onto one, so around 130GB of data that was previously on server B was added to server A.  Up until that point, server A was regularly backed up by DPM1 and then replicated to DPM2, but since that extra data was added, DPM1 backs the server up but the replication to dpm2 never completes.  The data rarely changes, so if I can get the initial replication to finish, the nightly updates should be no problem. 

    (A couple of other servers also have trouble replicating, but that's because DPM seems to want to move the entire BMR image across the wan every time, rather than only replicating changes.  I've asked about that issue here in the forums before, but never could get an answer, so I try to make sure those replicate successfully on weekends when there's a longer period of time available for them to run without affecting users.)

     

    Tuesday, December 27, 2011 3:58 PM
  • Hi,

    Q) Under normal circumstances, a consistency check doesn't transfer the data in it's entirety over the network does it?


    A) No, DPM will only transfer file data that is new or changed.   However, it does need to check each file on the primary DPM server and make sure that the secondary’s copy identical, so that will require time to perform those checks.  

     

    If the amount of new data is large and eating up the limited bandwidth doing the transfer, then you can benefit from pre-seeding the replica volume on the secondary so only delta changes between the backup to tape and restore from tape are transferred during the consistency check. 

    As far as BMR is concerned, the reason why the secondary DPM server seems to replicate the whole BMR image each time is due to the way BMR is performed on the Primary. Windows Server backup on the protected server "overwrites" the entire BMR backup image .vhd file(s) on the DPM server, so the DPM Filter tracks those overwrites and the secondary needs to bring them over and apply the writes to it's copy, basically overwriting the entire image vhd file(s).   So we are only bringing over changed blocks, but every block has changed due to the overwrite method of BMR backups.


    Regards, Mike J. [MSFT] This posting is provided "AS IS" with no warranties, and confers no rights.
    Tuesday, December 27, 2011 4:30 PM
    Moderator
  • Ok, that helps.  So if I can seed the replica on dpm2 manually, that should help.  How would I go about doing that, considering that the protection group on DPM2 is pointing to DPM1, not directly to the original drive on the file server?

     

    Regarding the BMR issue, thanks for the insight.  I've asked before in the forums, and I know others have as well, and never did get an answer.  Just to be clear, you're saying with dpm2010, bmr backups replicating to a secondary dpm server will always transfer the full system image, as opposed to just the actual data that changed on the original server.  Is that correct?   Will that be changing in dpm2012?  

    It does seem kind of odd that the 'disaster recovery' functionality of dpm, offsite replication, wouldn't work well with BMR backups, considering that BMR images would be the most desirable backups to have available in case of a disaster...

     

    edit: FWIW, I found one of the previous threads about the bmr issue:

    http://social.technet.microsoft.com/Forums/en-NZ/dpmssandbmrbackup/thread/ebb1f884-c44b-435b-a9eb-a5f5235e6e9b

    Tuesday, December 27, 2011 4:45 PM
  • Hi,

    If you have a tape drive on both DPM Servers, you can take a long term backup of the file data from the Primary DPM server, then ship the tape to the offsite location.  On the Secondary DPM Server, the tape will show as imported.   Re-catalog the tape then under the External tapes tree under the recovery tab, you can restore the data to the replica volume, exactly the same way as you would do it for a manual replica load.  Then start a new consistency check.

     

    <snip>
    Just to be clear, you're saying with dpm2010, bmr backups replicating to a secondary dpm server will always transfer the full system image, as opposed to just the actual data that changed on the original server.  Is that correct?   Will that be changing in dpm2012?  
    >snip<

    This is not a DPM problem, DPM is bringing over all the blocks that changed on the primary DPM server as a result of the Windows server backup overwriting the .VHD file(s) - DPM is working properly, so there is no change in DPM 2012.

     


    Regards, Mike J. [MSFT] This posting is provided "AS IS" with no warranties, and confers no rights.
    • Marked as answer by NeighborGeek Tuesday, December 27, 2011 6:25 PM
    Tuesday, December 27, 2011 6:14 PM
    Moderator
  • Thanks, I'll try that.  I didn't know if it would work the same as if I were backing the file server up directly to dpm2.  

     

    Re: BMR's -- I don't know, within Microsoft, which product group's "Problem" it is, but to me, it's an undocumented defect in DPM.  We bought the product based on available documentation, which says that only changed blocks are replicated to the secondary server.  It didn't say anything about this not working with BMR.  I do understand your explanation, that technically every block is changed, but from the customer point of view, it's not working as advertised. It doesn't really matter to me whether it falls on the shoulders of the DPM team to find a way to detect changes within the backups, or on the windows team to not re-send the full image each time, I just want it to work.  

    (Sorry, don't mean to rant.  It's just been an issue for a while, I'm glad to finally have an answer, even if it's just an explanation of why it works the way it does, and that there are no plans to fix it.  I've been working around the problem for almost a year, and will continue to do so.)


    If the issue won't be fixed by DPM2012, do you know if it is something that is being addressed by the windows team for Server 8?

    Tuesday, December 27, 2011 6:25 PM
  • Mike -- After thinking about it, I have one more question on the BMR issue.  DPM doesn't save each instance of a BMR as a full image, does it?  Meaning, a nighly BMR backup of server A isn't going to take up 20GB of disk space on DPM tonight, another 20GB tomorrow, and 140GB total to keep 7 days worth of backups.  I thought I understood that DPM gets the full image from the protected server, but then analyzes it somehow and only stores the changes.  Is that what is happening?  And if so, Why couldn't the secondary DPM server collect only the data that the primary DPM server determined had changed?
    Thursday, December 29, 2011 7:32 PM
  • Hi,

    DPM relies on the Windows volume shadow copy service (VSS) to maintain previous versions of file data.  It does this by performing a "copy-on-write" (COW) operation.  When a write comes in to overwrite a block on the replica volume, VSS reads that block and calculates a CRC of the block.  It compares the CRC with the data to be written, if they are different, VSS knows that it needs to preserve that block so it writes it to the recovery point volume.  It does this read / compare and copy if necessary for every block write done on the replica volume.   This is why the recovery point volume does not have to keep a full copy of the VHD coming over from the protected server.  

    The DPM file system filter driver on the DPM server just tracks writes, it does not do a read  / compare operaton for every block written and not track changes for like blocks. That would cause excess IO and not add any real benefit, so consequently files like BMR VHD's that may have lots of duplicate blocks every time are added to the changed block bitmap and need to be transfered each time to the secondary. 


    Regards, Mike J. [MSFT] This posting is provided "AS IS" with no warranties, and confers no rights.

    Thursday, December 29, 2011 7:48 PM
    Moderator
  • Thanks Mike.  I appreciate the detailed explanation.  I hope someday MS (whether dpm or windows or some other group) will offer some kind of solution for this so that offsite replication of BMR's are more feasible.  In the mean time, I'll keep cancelling the jobs that are still running at start of business, and making sure they are completing successfully on the weekends.  

    (There's not any way to only run such jobs on weekends, is there?  Last I had looked, I think the max interval was 24 hours...)

    Thursday, December 29, 2011 8:31 PM
  • Okay, I'm trying now to restore the backup from a tape (made on dpmserver1) to the replica volume on dpmserver1.  Can this be done directly, or does it have to be restored to another local volume first, then copy that over to the replica volume?  The system drive on this DPM server doesn't have enough space to restore this, and the entire san at that site is dedicated to dpm, so if I have to restore it to an alternate location first I may end up having to reallocate some san space or add additional storage just for a place to temporarily restore the data to before copying it to the replica volume.

     

    Also, these instructions on technet for manually creating a replica seem to be incorrect or at least missing something.  When I mount the volume as directed, I can't browse it.  I get an access denied message.  I was able to access the volume by taking ownership and manually adding myself to the security settings for the volume.  But since that's not described in the documentation, I'm not sure if that's what I was supposed to do, or if it's likely to cause issues down the road.

    Tuesday, January 10, 2012 5:27 PM
  • Hi,

    Since you are restoring from tape created on Dpmserver1, to the replica on Dpmserver2, you should be able to restore directly to the replica volume throught the mountpoint to the FULL folder.  Simply select "Restore to an alternate location", then browse to the replica volume.  IE: C:\Program Files\Microsoft DPM\DPM\Volumes\Replica\File System\vol_790db354-437c-429c-a3fa-6cc622326691\0127504f-bdd7-462f-874a-f7282327f521\Full

    Be sure to select the option to OVERWRITE existing version and apply security settings of the recovery point version.

     


    Regards, Mike J. [MSFT] This posting is provided "AS IS" with no warranties, and confers no rights.
    Tuesday, January 10, 2012 5:55 PM
    Moderator
  • The only option I have for destination is to copy to a network folder, and when I select a path, it says it will create a subfolder at that location for the restored data.  Am I missing something?

    Ahh, just tried again with file system backup, the first was a system protection backup.  Restoring from the file system backup did offer the option to recover to alternate location. 
    Tuesday, January 10, 2012 6:24 PM
  • Hi,

     

    OK , then the data source in question you are attempting to restore must be application data like exchange, or sql and not file data like a volume or share.  That is the reason why it wants to create the subfolder. So even after you do navigate to the relica and restore the data from DPM - you will need to cut and paste the data under the subfolder to the root of the path specified in the "Path to Replica" link. 

     


    Regards, Mike J. [MSFT] This posting is provided "AS IS" with no warranties, and confers no rights.
    Tuesday, January 10, 2012 7:33 PM
    Moderator
  • I would agree...this is a big missing component in DPM versus the Windows Backup. Windows Backup is a simple tool included in the OS. DPM is a relatively expensive component for offsite and local backup that is advertised as a true changed-block backup solution. BMR, the most critical component for D/R in a backup solution, doesn't work the way the tool is marketed. It would seem like a reasonably straightforward solution is for the filter driver in the DPM agent does the true CRC changed block write when the destination is the DPM server share. Since the technology exists in the VSS solution, why can't Microsoft apply this to the specicialized write to the DPM server done by the Windows Backup for DPM BMR?
    Rob
    Monday, January 23, 2012 4:05 PM