In a Storage Area Network (SAN), the migration of data from one storage system to another can have significant impacts on the performance and functionality of the storage environment. Pre and post-migration comparisons are useful in assessing the effectiveness of the migration and identifying areas for optimization.

Here are some key factors to consider when comparing pre and post-migration performance in a SAN:

1. Data Transfer Speed: One of the most important factors to consider is the speed of data transfer during the migration. A successful migration should result in minimal downtime and minimal impact on application performance.
2. Data Integrity: The migration process should ensure that the data is accurately transferred to the new storage system without any data loss or corruption.
3. Storage Capacity: The new storage system should have enough capacity to accommodate the migrated data and provide room for future growth.
4. Storage Performance: The performance of the new storage system should be at least as good as, if not better than, the old system. This includes factors such as read and write speeds, latency, and I/O operations per second (IOPS).
5. User Experience: The migration should be seamless for end-users, with no disruptions to access or use of data.

Overall, pre and post-migration comparisons in a SAN should focus on ensuring that the migration is efficient, effective, and seamless for all stakeholders involved.