Azure cross-region snapshot copy ramps bandwidth — don't linearly extrapolate early %
Estimating time-to-done for an Azure cross-region snapshot copy that just started
Default cross-region snapshot copy in Azure (az snapshot create --copy-start true) does NOT have a constant bandwidth — Azure ramps it up over the first few minutes as the copy gets going. If you read completionPercent shortly after starting and extrapolate linearly, you'll overestimate the total time by a wide margin. Concrete observation: a 64GB OS-disk cross-region copy reported 15% at the 10-minute mark (which linear-extrapolates to ~67 min total) but actually hit 100% only a few minutes later, total elapsed time ~15-20 min. Implication: stop watching the meter for the first 5-10 min, give it time to ramp, then poll. If you genuinely need consistent throughput from the start (or guaranteed faster speed), use --bandwidth-copy-speed Enhanced on the create call — most docs don't surface this flag prominently.
For Azure cross-region snapshot copy timing estimates, do NOT linearly extrapolate from the first completionPercent reading — Azure ramps bandwidth and the early % is artificially low. Wait at least 10 min before extrapolating, or use --bandwidth-copy-speed Enhanced for a faster, more predictable curve.