Review firewall settings such
as access control lists (ACL), or troubleshoot problems with network
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Introduction to Disk Bottlenecks on Windows Servers
This page will explain how to use performance monitor to log disk counters. I will also
recommend solutions to disk bottlenecks on Windows Servers (2003 or 2008).
Firstly, a homily to explain why you should always monitor these 'big four'
objects: Memory, Processor, Disk and
Network. Beware of monitoring one counter in isolation because that
can lead to the wrong conclusions.
One company thought they had a problem with slow disks on a Windows 2003 Server. Performance
monitor confirmed long queues and slow disk access times. Their
conclusion was that the bottleneck was the disk and so they bought faster
disks. Unfortunately, the slow response persisted and they called me in to
investigate. By monitoring all the 'big four' performance objects, I
found excessive paging, there was also less than 2MB of available bytes. The true
ailment was lack of memory, high disk usage was a symptom and not the cause. The
lesson: incomplete monitoring can mean a waste of time and money, so always
record these four objects:- Memory, Processor, Disk and Network.
The Windows server roles most likely to experience disk problems are, web servers
with lots of graphics and file servers. On the other hand, Domain Controllers, DNS,
or DHCP servers are unlikely to have disk bottlenecks
In Diagram 1 performance monitor shows classic symptoms of a disk bottleneck. My diagnosis is
based on the Disk write queue counter, you can see that this queue averages
more than 2. In fact the average is nearly 4 (with a peak of over 8).
I wanted to to be unbiased. So, to ensure that it was not a processor or memory bottleneck, I also recorded % processor time and available bytes.
As you can see from Diagram 1, the processor's average was below 30%.
If the processor were the bottleneck the trace would be over 80%. On the
other hand, if there was a memory shortage, available bytes should drop below 10MB.
The graph show there was always 70 MB of Available MBytes.
The
performance bottleneck may be worse than the average figures above suggest. In
Diagram 2, I have legitimately chopped the graph to isolate the period
of intense
disk activity. For these 5 minutes (4:46) the average is almost 6
against the bottleneck threshold of 2.
The other difference is
that in
Diagram 2 (taken from performance monitor), I have included % Disk Time, this exceeds 100% for the
duration of the trace. In other words, the disk is working flat out
writing data to to the hard drive.
There is one more deduction we
can make from the queue data on the chart. If you compare the
white line with the thick green line near the bottom, you can tell that the
disk is writing more rather than reading. To see the diagrams more clearly, double click and expand the thumbnails into larger diagrams.
Guy Recommends: A Free Trial of the Network Performance Monitor
(NPM)
SolarWinds'
Network Performance Monitor
will help you discover what's happening on your network. This
utility will also guide you through troubleshooting; the dashboard will
indicate whether the root cause is a broken link, faulty equipment or
resource overload.
Perhaps the NPM's best feature is the way it suggests solutions to network
problems. Its second best feature is the ability to monitor the health of individual VMware
virtual machines. If you are interested in troubleshooting, and creating network maps, then I recommend that you
give this Network Performance Monitor a try.
Once disks fill to 70% capacity they slow down dramatically. The other
side of the coin is that a defrag can cut queues in half. Incidentally, I
am always on the lookout for such cost-nothing solutions.
Starting with Windows 2000, Microsoft has licensed part of
Diskkeeper. What you can do is defrag a server drive-by-drive. What
you cannot do is schedule a defrag for the middle of the night, neither can you
select multiple drives for defragging. So the answer is to get a good
third party defragger like Diskkeeper's full product.
Faster disks
The logical solution is to buy faster disks. Go to your existing
disk manufactures site and compare their figures with the data you collect
for:
PhysicalDisk: Disk Read Byte /sec
PhysicalDisk: Writes /sec
Other Servers
Another cost-nothing solution would be to move the files or database to
another server. Alternatively you could use the load-balancing
properties of DFS.
Disk Striping
This would be my least favoured option. Technically it is a neat
idea, to stripe data across two or more disks. The principle reminds
of school days when I had to write out, 'I must not run across the school
grass' 500 times. To speed up the process I wrote my lines with 3 pens at once.
The multiple disk controllers, like my pens, write simultaneously across
three disks. The reason I am wary of this method is that there is no
redundancy, if any one disk fails you would lose all the data. Of
course you could use hardware RAID 5, 10 or 20 which would protect your data
against one disk failing.
Diskperf's overhead is very small and my advice is to leave it turned on.
Another
hint that this is the correct approach is that Windows 2003 has diskperf on by
default. If you have Windows 2000 and you do not set diskperf -y then you
are storing up a problem for when you ever do need to measure disk performance.
The problem is that setting diskperf needs a reboot and it would be most inconvenient
when you are keen to get on with the troubleshooting.
Perfmon situation 2000 and 2003
DISKPERF [-Y[D|V] | -N[D|V]] [\\computername]
-Y Sets the system to start all disk performance counters
when the system is restarted.
-YD Enables the disk performance counters for physical drives.
when the system is restarted.
-YV Enables the disk performance counters for logical drives
or storage volumes when the system is restarted.
-N Sets the system to disable all disk performance counters
when the system is restarted.
-ND Disables the disk performance counters for physical drives.
-NV Disables the disk performance counters for logical drives.
\\computername Is the name of the computer you want to
see or set disk performance counter use.
The computer must be a Windows 2000 system.
NOTE: Disk performance counters are permanently enabled on for
systems beyond Windows 2000.
Be aware that with Windows Server Disk monitoring there are both physical and
logical disk counters. Disk activity could mask memory shortage, so always monitor the 'big 4' counters, Memory, Processor, Disk and Network.
If you like this page then please share it with your friends
Learn
the secrets of which counters to monitor. Master performance monitor
logging,
develop your skills with structured exercises and examples. Print
out a copy to read, while you design logs and alerts to detect network
bottlenecks.
Guy Recommends:
SolarWinds' NPM - Network Performance Monitor
SolarWinds' performance monitor is designed for detecting network outages,
making it easy to see what's working, and what needs your attention.
This utility guides you through creating network maps; it also helps
identifying whether the
root cause is faulty equipment, or resource overload. Give NPM a try.
Learn
the secrets of which counters to monitor. Master performance monitor
logging,
develop your skills with structured exercises and examples. Print
out a copy to read, while you design logs and alerts to detect network
bottlenecks.
