The purpose of this article is to provide prescriptive guidance on how to troubleshoot logical and physical disk response times in regards to Windows performance analysis.
Start with the following performance counters to analyze disk response times:
These counters are generally the first ones to look at because we are looking for the following attributes of the Input/Output profile:
This article is grouped by symptoms, then by possible causes.
How to Diagnose
Possible Solutions and/or Recommendations
Storage response time reduced because of misaligned partitions.
High disk fragmentation
Lack of free space
Insufficient number of disks
Flooding the I/O channel and causing retries or “busy” from the storage device
Low throughput, high number of transfers
Perfmon Log Capture Interval: Generally speaking, if capturing performance data on a live system using the Windows Performance Monitor, the sampling interval should be kept fairly non-intrusive, such as every 10 seconds. The problem with sampling at 10 seconds or longer is that we tend to miss a lot of data. If in a testing environment we should set the capture interval to 1 second and capture both Physical Disk and Logical Disk counters. If we are capturing at short intervals like 10 seconds or less, we may not want to capture other counters at the same time so as to not impose too much overhead on the system for performance monitoring.
Capturing Logical Disk versus Physical Disk Counters: The other thing to keep in mind with Performance Monitor is that if we are gathering performance data, there is a cost in performance associated with gathering a specific performance counter. At the same time there is little additional host performance cost to go ahead and capture the entire performance object. The point being that when measuring storage performance, go ahead and capture Physical Disk and Logical Disk objects and not just individual performance counters. If the physical disks only have 1 partition per disk, then there is really no need to capture the Logical Disk counters. The exception being of course if you are making use of Mount Points within Windows and you need to measure performance of individual physical disks.
When capturing performance data, there is sometimes a concern about the size of the capture file. If capturing only Physical Disk and Logical Disk counters, even at a 1 second interval, the resulting file will not get to be excessively large. For a cost of 100 MB or so, and depending on the number of disk devices. If capturing only Physical Disk and Logical Disk counters, even at a 1 second interval, the resulting the counter log file will typically not grow, excessively large, perhaps 100 MB or so, depending on the number of disk devices.
Written By: Robert Smith
Contributors: Clint Huffman, Jimmy May, and Ken Brumfield
Thanks, Clint. Terrific content as usual. Use Clint's PAL tool for help with analyzing perf data:
Why would you use LogicalDisk and not PhysicaDisk? Specifically if you are monitoring I/O, wouldn't looking at LogicalDisk prevent you from really knowing what's going on?