SCSI disk not detected during boot process

[tzx17077]

I try to make my TCS 15.0 64bit virtual machine ready for the Azure cloud but face some issues with changing my disk controller type to scsi: I remastered my initial ramdisk to contain the kernel modules required to support scsi drives (scsi extension module) and ran depmod before remastering but when I boot with extlinux it does not detect the scsi sda and thus is not able to load extensions. Only when the boot process is already finished it seems to detect scsi drives.
What am I missing?

[curaga]

Could be just timing, sometimes scsi is slow. Your dmesg should show when things happened.

[tzx17077]

You were perfectly right Curaga, I added waitusb to the boot options and now it‘s working fine.
Thanks.