When a share is created, it will automatically begin migrating in the background,
in addition to servicing inline requests. This migration is controlled by the shadow
migration service. There is a single global tunable which is the number
of threads dedicated to this task. Increasing the number of threads will result in
greater parallelism at the expense of additional resources.
The shadow migration service can be disabled, but this should only be used for
testing purposes, or when the active of shadow migration is overwhelming the system
to the point where it needs to be temporarily stopped. When the shadow migration
service is disabled, synchronous requests are still migrated as needed, but no
background migration occurs. With the service disabled no shadow migration will ever
complete, even if all the contents of the filesystem are read manually. It is highly
recommended to always leave the service enabled.