If your computer overall performance is degrading and you suspect that one of your hard drives is the cause then you need a tool that helps you monitor the performance of your hard drives. Windows 7 in-built Performance Monitor helps you identify bottlenecks and can be used to monitor disk performance.
Disk Quotas allows administrators to control how much of a volume users can fill with files. Although, disk quotas are normally implemented on servers that hosts shared folders they can also be implemented on standalone computers running Windows 7. In a scenario where multiple users access a single computer, a single user may completely fills a volume with his/her files hence, preventing others from saving their files due to lack of storage space.