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Why does my backup take so long to complete after a reboot or restart?

Question

Why does my backup take so long to complete after a reboot,
and what is this integrity check I see in the history?


INFO 01/01/2009 00:00:00 CST (tid:253) AGENT: Accepting new backup request for (Disk 1 Partition 0) INFO 01/01/2009 00:00:00 CST (tid:253) AGENT: Changes have not been tracked for this device. Forcing checksum verification. INFO 01/01/2009 00:00:00 CST (tid:253) Performing full partition integrity check. INFO 01/01/2009 00:00:00 CST (tid:253) Sending MD5 sums from last recovery point. INFO 01/01/2009 00:00:00 CST (tid:253) Sending MD5 sums finished.

Answer

It's totally normal for a integrity check (full block scan) to take HOURS and take about as long as it took to complete the initial replica.
We have to read ALL allocated file system blocks from disk. We send deltas (changed blocks) as we find them.
This means its totally normal for the transfer rate to appear slow... its because we send deltas here and there as we find them not all at once.
If we instead... read all blocks first to find deltas then reading them again to send them would make transfer rate look fast but task would take roughly twice as long!
You don't get benefits of high performance CDP backup when you have to do a block scan.... and that's totally normal...


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