The queries still seem slow immediately after sn

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The queries still seem slow immediately after snapshot creation. Why?

You have a SQL Server 2005 sales database experiencing performance problems because of heavy I/O activity. You decide to create a snapshot of this database every hour, stored on a separate physical disk array and use that for reporting queries. However the queries still seem slow immediately after snapshot creation. Why?

Answer
The snapshot still queries the original database.
Explanation
The snapshot of the production database will only reduce I/O for changed pages. Any data that has not been changed will be read from the source database, which is in this case is experiencing heavy I/O itself.

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