Is my hard drive healthy?

The hard drive is rarely considered the primary cause in bottleneck cases; we usually tend to suspect the applications installed on the server.

People often think the source of system performance issues is either disk corruption or insufficient disk space, but Physical Disk: %disk time and Physical Disk: Current Disk Queue Length are equally important metrics that work in parallel. There are few other ways to detect hard drive problems using other metrics, but for now I will only focus on these two performance counters.

Physical Disk: %disk time monitors the percentage of time that the disk is in use. If it runs over 90%, then the system is struggling.

Physical Disk: Current Disk Queue Length indicates both the number of requests being served and the number currently waiting for disk access. This number should fluctuate, and not exceed 1.5 to 2 times the number of spindles¹ that make up the physical disk.

Figure 1: shows a healthy hard drive. Notice the Current Disk Queue Length (green line) is sometimes high, but it’s not an indication of a bottleneck since the %Disk time (red line) is below 90%.

Figure 2: When the peak stalls at high number, e.g., +90% (the vertical red line), then you must monitor the Current disk queue length (red circle). If the queue length number exceeds 2 or 4 (depending on the number of spindles), this is a good indication of a bottleneck.

Solution:

If you confirm that the hard drive is having issues, here are some steps to follow:

1-      Run a defrag on the server: it is strongly recommended to do this OFF hours

2-      Move some heavily used files and folders  to another disk (not a partition) or another server, such as log files and the mail queue (if possible)

3-      Run the command CHKDSK (without /F) to see if you have any disk problems

4-      If you are using RAID, make sure that you are using  write-back mode

5-      Or, finally, get a new hard drive with a higher rpm (10000 or 15000 rpm).

¹ The spindle is a shaft that holds the hard disk assembly and rotates the platter(s) at a speed that ranges from 5400 to 15000 rpm