Comment 11 for bug 1925722

> Curtin doesn't respect "custom" config of the storage and follows "simple" flow and deploys the OS on "sda", more precisely to the first block device in the array (see last two lines of the log below)

MAAS and curtin only support writing custom images as opaque blobs with DD. When the image is dd-* type, curtin deploys via meta_simple as it's going to just write out the image to the specified target device.

As with all curtin configurations you should specify the disk serial number of the target disk on which you expect to install your image.