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A colleague has raised a question which I'm hoping might be answered here. He is testing Veeam 4.1 on vSphere ESXi 4 Update 1 servers which use local storage. He found that after the initial full replication, the subsequent incremental replications were much larger than expected. Even after moving the pagefile onto a seperate drive and excluding this, the Veeam reports showed a much greater data replication volume than expected. He was testing with a view to providing replication across a 10MB leased line for DR, but has concluded it does not seem viable.
The theory posed was that although a minor amount of data was changed within the Windows guests, the complete VMDK block that data resides in is being copied each time. So a few bytes changed in an NTFS file could equate to a 1/2/4/8 MB copy per block. Is that how it works?
Discussion also revolved around that issue the a near CDP replication schedule would mean the hosts guests are in an almost permanent state of snapshot and concerns were rasied about that.
I had suggested Veeam to the department initially and don't want to see it discounted without understanding these items in more detail. We are traditionally a Double Take house using DTVRA to replicate guests at the guest level, but we felt Veeam offered a cleaner (and lower cost) solution. Anything I can suggest to kickstart the evaluation again or just clarify the raised questions would be of help.
Thanks in advance.
- SVP, Product Management
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Today for most typical workloads we are seeing that replicating every 15 minutes usually result in incremental replications to complete in under 1 minute over decent link even with the current block size, but of course for very I/O active servers you may want to consider lowering replication frequency because they those may take up to 5 minutes to process the changes today. Of course, using slower WAN links also affects these timings accordingly.
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