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The problem:

Our server database contains 1TB of data. It runs on a Sybase ASE 15.7 server and shall be migrated to SQL Server 2014. The servers will be located in the same data center during migration; an acceptable downtime is 6 hours.

We have considered using Sybase Replication Server, as we understand it, this product supports heterogeneous database replication from ASE to SQL. However; we do not have experience with this. Snapshot and transactional replication might be a possible solution.

We have some experience with SQL Server Migration Assistant and have successfully migrated the database objects and data in a test environment. However based on 8% test data, we have estimated that a complete migration of production database will take about 7 days. We can only have 6 hours downtime, and are not sure if this product can be used for data migration in our case. For database objects, this product has worked fine.

Do you have some recommendations to solve this problem?

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Is there a way for you to segregate the data into stale and active and then migrate in tranches? In my experience large databases have upto 70% data that is there for historical reasons - reporting, analytics etc., which, if you can identify, can be moved ahead of time.

In other words, Can you identify the tables that do not change regularly and migrate them first? If that is not feasible, do the transactional tables have date fields in them so you can migrate the data upto a point and then migrate the rest of the rows during the cut over?

The problem you will face with Sybase replication is that you will have to get the databases to a mirror state before you can sync the queues. With a very large database with heavy transaction load, that could be difficult. In your case, by the time the database gets migrated, it will be 7 days or more assuming nothing fails and you will have to forward play the 7 days worth of transactions via the replication queue which will need to be big enough to accommodate all this, assuming you will not get any conflicts with RDBMS specific conversion issues.

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Note that the ASE-to-MSSQL Sybase (now SAP) Replication Server product is discontinued. Here are details from a posting in the SAP Replication Server community forum:

EDCA (Enterprise Connect Data Access) / Replication Server Heterogeneous Edition are no longer avaialble. See https://me.sap.com/notes/3408368 and https://me.sap.com/notes/2702069

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