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I have configured perfmon in order to see if the server disk has a problem.

  • The Avd Disk Write Queue Length is the white line
  • The % Processor is the black line that was never over 50%

From what I know this should never happen unless the disk has a problem.

Am I correct? Please advise.

enter image description here

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migrated from Nov 17 '11 at 13:57

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It seems that Sql server is continuously writing in tempdb. I have managed to identify a query that makes Sql server to write 55MB in tempdb each time is executed. I guess this makes the disk to respond so slow. Is this correct? How can I troubleshoot this issue? – johnny Nov 18 '11 at 12:05
Do you have any other discs you can move the TempDB files to? Are all the SQL database files ob the same volume as your system files and website directory? – Top__Hat Nov 18 '11 at 12:32

Cannot see a white line. Keep an eye on your scaling. Your Scale for the queue length is set to 100. Means a measurement of 1 is displayed as 100. Anyway the average is 62 with a maximum of 819 which is way to high. Seems in fact that you've a kind of I/O bottleneck.

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I've updated the graph. Thanks – johnny Nov 15 '11 at 13:56
Oh yeah. Way to high. Means a disk queue length of up to 1000 outstanding I/Os. Wondering whether the system can still work under this cirumstances. I suspect no. What happened? Is it a single hard drive? SAN? RAID-Set? – Anja Nov 15 '11 at 14:19
There is only one hard drive. The system is working but the website that's hosted on it is barely responding. Is there a straightforward way (tool) to find what is being written on the hard drive? – johnny Nov 15 '11 at 14:30
You can use the Sysinternals ProcessMonitor for tracing in realtime what happens / which files are written by which process. The tool itself will need additional ressources of course. Did you check your windows event log for drive / filesystem failures? – Anja Nov 15 '11 at 14:45

I’m thinking that this is more a problem with the physical disk. Have you checked for Disk Fragmentation? Also have you run a checkdisk? This might shed some light any on physical problems. You say the website isn’t responding. Does it do this when you access the website locally? Or just external from this server?

Sorry to ask more questions in an answer.

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I tried a defragmentation...nothing changed. – johnny Nov 18 '11 at 12:05

Impossible to answer because we lack all the information. Queue length in general is totalyl useless as a counter - subsytems can have large queues without getting slow.

There is another set of cuotners which says seconds / read or seconds / write. This (*1000 to get milliseconds) is mrore usefull. I dont care how long the queue is - i care when I overlaod the drive which is when the response time gets slower.

It is a misconception that people think queue length without a LO of interpretation and additional inforamtion is usefull.

Want an extreme? I know of a sql server having 255length disc queue.... to every of itÄs nearly 30 discs. It has 30 discs to be able to put in larger total queues as thje drivers only allow 255 maxium for one disc.

Bad? well, the uplink is multiple 8 gigabit fibrechannels to a 160 disc HP EVA SAN with 32 gigabyte cache. Response time is STILL1-2 milliseconds ith those queue lengths. SO, the length is totally useless here. The seconds / x gives an imediate answerable number without a lot of interpretation.

Update: if that is hat you asy- single disc, probably SATA, then yes, the lenghts are way too high, your IO is tottaly overloaded.

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Perfmon counters update: link – johnny Nov 18 '11 at 12:01

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