This was reported by @jhowardmsft on slack. He noticed that with newer kernel, specifically 4.14.53, the first pull on fresh data root is a lot slower than on older kernels, specifically he tested 4.14.23. Apparently the mkfs.ext4 seems to take a lot longer. One suspicion is the inclusion of 0020-scsi-storvsc-Allow-only-one-remove-lun-work-item-to-.patch and 0021-scsi-storvsc-Avoid-excessive-host-scan-on-controller.patch, which were introduced with 4.14.30 as part of some other debugging effort around LCOW and disk hotplug.

This is issue is to track the debug