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Joined: May 13, 2010 7:01 am
Full Name: Richard Ramshaw

1st Replication after upgrade to v7 hardware

Post by RichardR »


I have a query about how Veeam deal with the first replication (of an existing machine) after CBT has been enabled in v7 hardware as this will affect our scenario.

When there is no CBT Veeam checks for changes by reading the source disk and checking if it's changed (by checksum?), if so it sends the change to the destination.
In CBT though VMware gives the list of changed sectors and Veeam copies these sectors.

In an upgrade to v7 hardware the responce from VMware to an initial CBT enquiry is that 'all sectors' have changed (well actually just the non-empty ones) as it does not know what has or hasn't changed as the machine used to be v4 hardware. (this is from the VMware documentation)

Thus the query is: will Veeam therefore copy the entire machine again as a change (because vmware told it to) or does Veeam additionally check that a sector is actually different (with a checksum) even with v7 hardware and CBT enabled.

We have about 10TB of servers that are about to be upgraded to v7 and this will therefore make one hell of a difference to our WAN useage for the replication!



Vitaliy S.
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Full Name: Vitaliy Safarov

Re: 1st Replication after upgrade to v7 hardware

Post by Vitaliy S. »

Hello Richard,

I believe that after an upgrade to hardware version 7, on the next job run Veeam will still be comparing blocks to blocks on the source and target VMDK files as it did before, while not using VMWare CBT. But on this run we will recieve a ChangeID value, so it can be used on the 3rd run though.

Also please note that we will not copy an entire machine on your 2nd run, we will only transmit changed blocks, but it will be just a little faster than copying an entire VM because Veeam Backup will need to read the whole source VM image in order to be able to determine changed blocks since the last run.

Thank you!

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