Why is my migration running at speed X when my network speed tests report Y?

Comparing your mailbox migration speed with the result of a bandwidth test is comparing apples to oranges. A network speed test generates random bytes in memory and checks how quickly the data can be transferred. A speed test does not convert data, encrypt data, parse data, convert data, index data, read data from disk, write data to disk, or authenticate users.

Mailbox data is stored on disk. When we retrieve mailbox data, it must be read from disk. When we write mailbox data, it must be committed to disk. To access this mailbox data, the caller must be verified and authenticated. When data is written, it may be indexed. Mailbox data often also needs to be converted between systems.

Mailbox data is typically encrypted during transfer. Mailbox data must be encapsulated in protocol packets in order to be transferred over a network. Mailbox data must be parsed, for example to verify it contains valid MIME, to check if it contains a virus or to determine if it should be classified as spam. Mailbox data can contain hundreds of properties that must be analyzed and stored.

MigrationWiz will only open one connection per mailbox. This ensures we can scale to a large number of concurrent mailboxes. A speed test will try to fill your entire bandwidth, pushing streams of random bytes in parallel. While a faster connection will result in a faster migration, raw network speed is just one of the many factors impacting your overall migration speed.