Applications that perform asynchronous cached I/O read requests and that use a disk array that has multiple spindles may encounter a low performance issue in Windows Server 2008, in Windows Essential Business Server 2008, or in Windows Vista SP1
Consider the following scenario:
- You have a storage area network (SAN) disk array or a direct attached storage (DAS) disk array that has multiple spindles.
- The disk array is installed on a computer that has one of the following Microsoft Windows operating systems installed:
- Windows Server 2008
- Windows Essential Business Server 2008
- Windows Vista Service Pack 1 (SP1)
- An application uses the disk array to perform concurrent asynchronous I/O requests on this computer.
In this scenario, the application may have very low I/O read performance.
For example, you run SQL Server Analysis Service (SSAS) for an OLAP query on a Windows Server 2008-based computer. This computer has a disk array that supports concurrent I/O reads. SSAS uses 20 spindles to perform an asynchronous I/O read. In this example, you may find that the OLAP query performance in the Windows Server 2008 system is very low and that the system seems to have only 2 spindles working on the I/O request.
For more information on this issue, including potential causes, workarounds, and resolutions, see: Microsoft KB Article KB961719.