If you are experiencing problems due to disk contention and other problems related to object placement, check for these underlying problems:
Random-access (I/O for data and indexes) and serial-access (log I/O) processes are using the same disks.
Database processes and operating system processes are using the same disks.
Serial disk mirroring is being used because of functional requirements.
Database maintenance activity (logging or auditing) is taking place on the same disks as data storage.
tempdb activity is on the same disk as heavily used tables.