Migration speed

In certain situations, users might notice that process of both gathering and uploading data takes longer than expected considering the network bandwidth. Multiple factors may impact speed of the migration.

Where to install

First of all, software installation location may have an impact on the migration speed.

In the case of migrations from Exchange, CodeTwo strongly recommends installing the migration software directly on the source Exchange Server. Installation on other servers or workstations is fully supported, however, in this scenario the migration speed might be affected by the fact that data extracted from source Exchange mailboxes must be transferred over the local network to another machine where CodeTwo software is installed. This usually is not an issue but in some cases might be. Also, some organizations set up different Internet access speeds for their Exchange Server machine(s) and different for users' workstations. Installing directly on the server you avoid stumbling on such a problem.

The above advice, however, might not be the best one in these cases:

  • The source server machine is a very old, slow computer with small RAM amount (e.g. 2 GB). If this is how your source server looks like you may stumble upon problems related to the source Exchange Server machine performance.
  • The source server is equipped with an unsupported version of Windows / Windows Server (older than Windows 8 / Windows Server 2008 R2 SP1). Running the software on such versions of Windows may lead to various errors.
  • The source server does not meet the minimum system requirements.

If any of the above scenarios apply, we recommend installing the software on a workstation or dedicated server with better hardware and newer operating system.

In migrations from Office 365, which are handled via EWS, you can install on any machine with connection to both the source and the target, but we recommend that you install the software directly on the target Exchange server to achieve the best performance.

In the case of migration from a hosted Exchange server, the software can be installed on any machine with the connection to both source hosted Exchange server and target Exchange Server. However, we recommend installing it on a target server, to maximize the upload speed.

When migrating from an IMAP source, you can install the software anywhere you want. Source server-side installation is crucial only for migrations from Exchange Server (via MAPI or EWS). IMAP, on the other hand, is designed to be used over the Internet, so IMAP sources can be accessed from workstations outside of the source environment. So, when migrating from IMAP source, check which Internet connection is slower - to the source server or to the target server, and preferably install within the environment to which outside connection is faster. This will let you avoid using that slow connection.

Better hardware = faster migration

The software does not have any special hardware requirements, but there are a few hardware improvements that may considerably speed up the migration process.

First of all, use network adapters that handle the highest speed. Additionally, to eliminate other possible bottlenecks, make sure that your whole network infrastructure, including routers and switches, can support higher throughput. Keep in mind that the used network devices will not solely affect the migration speed. You need to take the download and upload speed into consideration as well. Internet Service Providers (ISP) often offer contracts with asymmetric connections (the upload speed is considerably slower than download speed). When talking about your Internet connections speed, you must be sure you are referring to the upload value as well. Symmetric links (upload = download) are often offered for business clients, but there is another catch – offered speeds are maximum possible speeds rather than guaranteed ones. For more information, please check your Internet access contract or discuss that with your ISP directly. Make also sure that the machine used to perform the migration has the highest network bandwidth available.

The whole software is optimized for a 64-bit architecture as 64-bit systems allow addressing more than 4 GB of RAM (32-bit systems are also supported, but they will probably work slower). The software can work with just 2 GB of RAM, but more RAM allows loading more items to the memory, which speeds up their processing.

If the network speed is not a problem and there are no other obvious obstacles, the migration speed will directly depend on the number of logical processors in the system. This number is particularly important in the case of migrations via the MAPI protocol. More logical processors allow more migration threads to be executed at once; hence the migration will run faster. You can also manually increase the number of threads in advanced settings, regardless of the number of logical processors, but doing so may not necessarily yield the expected results.

Coexistence of other MAPI-using software might be a problem

Source Exchange Server data is accessed by CodeTwo software via MAPI libraries or Exchange Web Services. When connecting via MAPI, it might be a good idea to make sure there is no other MAPI-using software enabled during the migration. It is not really required to disable third-party MAPI-using applications in the same environment, but if the other software performs many Exchange operations via MAPI the same time you migrate, this can affect the migration speed as both applications will have to share Exchange's time.

You actually migrate 30% more data than you have

Every single MAPI- or EWS-extracted item is converted by CodeTwo software into the Fast Transfer Stream (FTS) format, applicable for a particular target Exchange Server version. The software calls EWS API methods on the target server, to allow native access to target Exchange's database and migration without the necessity to install any additional applications on the target server. All calculations of the items’ sizes are based on final FTS binary files. The communication between your machine and the target server is done using the SOAP protocol, which works in the Request–Response mode. Prior to item dispatch, its FTS buffer has to be transformed to the Base64 format. Also, additional XML file with entries required by SOAP protocol is added to the transferred data stream. As a result, the size of every item is increased by 30% on average. Be aware that batches of items cannot be compressed due to SOAP protocol limitations.

Lots of small items migrate slower than big items

By default, every batch sent to the target server contains 150 items regardless of their overall size and requires opening a new connection. Consequently, a batch may be completed very quickly, containing e.g. 150 small text-only messages with a total size of only 3 MB. This may result in pulling many small batches within short time range and in effect lead to performance issues on the target server. After receiving a batch, every item requires individual processing by the Exchange Server. Therefore, you can observe that the migration speed slows down after some time when migrating lots of small items as the target Exchange is trying to cope with processing them. Migrating batches of small items is also slower in general due to the fact that both ends of the transmission exchange the so-called handshakes very often (i.e. the time spent by both source and target server on establishing and closing a connection for every batch separately).

Target Exchange's EWS throttling affects the speed too

We have also observed that despite the target server being capable of receiving many batches at the beginning, the migration process may start to slow down after some time. This behavior is normal and is due to target Exchange Server applying throttling policies.

Other ways to speed up the migration

If you believe that your migration process is too slow, please consider following the steps below:

  1. Move the migration software to another machine. If it was installed directly on the source Exchange Server, perhaps its hardware performance is too low - find a faster machine and install the program there. If it was installed on a workstation, maybe you have stumbled upon a local network related issues - do the opposite, install directly on the source server. In any case, before installing somewhere else, familiarize yourself with our Knowledge Base article on how to move installation safely.
  2. Perform a staged migration. Instead of migrating all data at once, you can migrate items only from e.g. last 90 days. Thanks to that, your users will be able to start working on the new server without any interruption, while you can comfortably finish migrating older items later.
  3. In the case of on-premises Exchange Server, you can apply optimized throttling policies to increase the speed. Although you cannot do the same in Office 365 (Exchange Online), it is still possible to temporarily ease EWS throttling policy limits. Refer to this article to find out more.
  4. CodeTwo software comes with the migration parameters preconfigured by the developers to maximize the migration speed based on our research, tests, our own experience, as well as suggestions from our clients. However, it is difficult to expect exactly the same set of parameters to be actually optimal for all possible scenarios. Therefore you might want to try using different software settings to suit your needs. See our Knowledge Base article on that.
  5. If none of the above helps, contact CodeTwo Support, by following the steps from this article.

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