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DRBD HA between 2 VM guests, between 2 vSphere nodes.

Posted on 2016-09-01
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Last Modified: 2016-10-14
I've recently set up drbd to replicate logical volumes between two VM's.  Machine 1 comes out of the box and installs around 5GB, even though max size is around 50GB for the logvols.  When the 2nd VM comes on line, it syncs the data, whitespace and all, of the DRBD volumes even though thin disk provisioning is enabled.  It makes sense as DRBD is writing empty blocks to VM2, whereas out of the box, the volumes only contain filled space.  My question can be answered in two ways.  Is there a way to make vSphere recognize the white space on VM2 and shrink the volume or is there a way to tell DRBD to ignore white space (thin provisioning on the linux DRBD volume level)?

VM1 - 5GB
VM2 - 50GB
Both have the same file system and contents, VM1 has the mounted file systems.

Thanks in advance!
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Question by:Chris H
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4 Comments
 
LVL 80

Expert Comment

by:arnold
ID: 41780949
Drbd is a low level, media level replication, it copies/replicates bits it has no consept of files.
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Author Comment

by:Chris H
ID: 41782260
Still, isn't an emtpy block predictable enough to just set a marker instead of writing that empty block?
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Accepted Solution

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arnold earned 2000 total points
ID: 41782317
Drbd is a mirroring/cloning mechanism. I am not sure what you are after, often VMs on the same system would not use drbd but would have access to a space served by the host.
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Author Closing Comment

by:Chris H
ID: 41844322
There is no way to do what I've asked, so I will award points for Arnold's efforts.  The best solution is to minimize the size of the partitions and grow them accordingly.  DRBD only sees blocks, so a 20 GB partition with 1 GB of data will sync 20GB to a secondary node even if the disk is thin provisioned.  Bummer...
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