Click here to monitor SSC
SQLServerCentral is supported by Redgate
 
Log in  ::  Register  ::  Not logged in
 
 
 


High Avg. Disk Queue Length


High Avg. Disk Queue Length

Author
Message
Kwisatz78
Kwisatz78
SSChasing Mays
SSChasing Mays (607 reputation)SSChasing Mays (607 reputation)SSChasing Mays (607 reputation)SSChasing Mays (607 reputation)SSChasing Mays (607 reputation)SSChasing Mays (607 reputation)SSChasing Mays (607 reputation)SSChasing Mays (607 reputation)

Group: General Forum Members
Points: 607 Visits: 1821
Hi all

on a current logical volume in perfmon which is using a scalre of 100.00 my average reading is coming back as 1.860 which would indicate a value of 186 for he avg. disk queue length correct?

If this is so then its extremely high and is maximum reaches the thousands.

Other counters such as buffer cache hit averages 99.5% and Avg. Disk sec/read 0.013 and Avg. Disk sec/write 0.015 on a scale of 1000.00 which would indicate it to be 13ms and 15ms respectively which seems a reasonable speed.

In that case what could be causing the disk queue to be so high?

Thanks for any steer in the right direction.
SQLZ
SQLZ
SSC Eights!
SSC Eights! (874 reputation)SSC Eights! (874 reputation)SSC Eights! (874 reputation)SSC Eights! (874 reputation)SSC Eights! (874 reputation)SSC Eights! (874 reputation)SSC Eights! (874 reputation)SSC Eights! (874 reputation)

Group: General Forum Members
Points: 874 Visits: 940
Hi,

Actually the scale is only relevant when looking at the graph. So if you're looking at the graph and the value is 52 (for example) you should divide by the scale (not multiply).

Either way though, if you're actually looking at the values provided rather than the graph, those are the true values. So, if your average reading is 1.860 and you got that from the values shown then that's your queue length (divided by the number of disks in your raid configuration of course).

Hope that helps.

Karl
source control for SQL Server
Bhuvnesh
Bhuvnesh
SSCrazy
SSCrazy (2.9K reputation)SSCrazy (2.9K reputation)SSCrazy (2.9K reputation)SSCrazy (2.9K reputation)SSCrazy (2.9K reputation)SSCrazy (2.9K reputation)SSCrazy (2.9K reputation)SSCrazy (2.9K reputation)

Group: General Forum Members
Points: 2924 Visits: 4076
I also got the same kind of problem in one of my dev server,But no resolution till yet :-D

when do we get high spikes for "disk queue length".NO patch/SP/hardware change on this server

-------Bhuvnesh----------
I work only to learn Sql Server...though my company pays me for getting their stuff done;-)
Kwisatz78
Kwisatz78
SSChasing Mays
SSChasing Mays (607 reputation)SSChasing Mays (607 reputation)SSChasing Mays (607 reputation)SSChasing Mays (607 reputation)SSChasing Mays (607 reputation)SSChasing Mays (607 reputation)SSChasing Mays (607 reputation)SSChasing Mays (607 reputation)

Group: General Forum Members
Points: 607 Visits: 1821
Hi Karl - That was a useful explanation thank you.
NickDBA
NickDBA
Old Hand
Old Hand (361 reputation)Old Hand (361 reputation)Old Hand (361 reputation)Old Hand (361 reputation)Old Hand (361 reputation)Old Hand (361 reputation)Old Hand (361 reputation)Old Hand (361 reputation)

Group: General Forum Members
Points: 361 Visits: 936
Are you actually experiencing IO bottlenecks etc? A disk queue length of 1.86 doesn't indicate a problem on its own. A disk queue length > 2 (per spindle / indivual physical dislk) would suggest a bottleneck, although occasional spike are to be expected.

So, for example, a 2 disk RAID1 drive showing an Avg Queue Length of > 4 would be an issue, a 5 disk RAID5 showing an Avg Disk Queue Length > 10 would be an issue etc. Also check % Disk Time (>50%), and look for certain *IO* WAITYPES on processes to indicate Disk IO issues.
Ramji29
Ramji29
SSC Veteran
SSC Veteran (227 reputation)SSC Veteran (227 reputation)SSC Veteran (227 reputation)SSC Veteran (227 reputation)SSC Veteran (227 reputation)SSC Veteran (227 reputation)SSC Veteran (227 reputation)SSC Veteran (227 reputation)

Group: General Forum Members
Points: 227 Visits: 479
Just one more addition to this..... when we select the counters we've an option to select the individual drive (i.e. C or D etc) this will give more specific info if you run the counter by selecting your data or log drive rather than selecting the total one..... which will be the average of all the drives....

Rohit
Go


Permissions

You can't post new topics.
You can't post topic replies.
You can't post new polls.
You can't post replies to polls.
You can't edit your own topics.
You can't delete your own topics.
You can't edit other topics.
You can't delete other topics.
You can't edit your own posts.
You can't edit other posts.
You can't delete your own posts.
You can't delete other posts.
You can't post events.
You can't edit your own events.
You can't edit other events.
You can't delete your own events.
You can't delete other events.
You can't send private messages.
You can't send emails.
You can read topics.
You can't vote in polls.
You can't upload attachments.
You can download attachments.
You can't post HTML code.
You can't edit HTML code.
You can't post IFCode.
You can't post JavaScript.
You can post emoticons.
You can't post or upload images.

Select a forum

































































































































































SQLServerCentral


Search