How to know how many disks drives I have in an array? 1

[ericnet]

How can I know how many physical disks or disks drives exists in an array?

I don’t understand; What does ‘a disk drive in an array’ mean? And, ‘a physical disk’? And, ‘the number of spindles in physical disk’? A hard disk of a server can contain several physical disks?

I ask it because I am beginning to learn what does every performance counter in my Windows 2000 Server. Specifically, now I am trying to understand what does PhysicalDisk\Avg. Disk Queue Length counter, and the explanation I found in an article, which I don’ t understand very well, is this:

PhysicalDisk\Avg. Disk Queue Length
Threshold: Should not be higher than the number of spindles plus two.
Significance: This counter indicates the average number of both read and writes requests that were queued for the selected disk during the sample interval.

Thank you

 

[kmkeshav]

I try to put in my views (not sure I am correct!).

In a SCSI array, you have two views: one is the physical view (how the disk drives are physically connected in an array) and the second one is logical view (how you have logically split/partitioned your physical drives i.e., how many logical drives you have totally for all the physical drives in an array).

If you have installed Array configuration utility on your server, you can use this utility to view all these details. You can see how many arrays you have, how many physical drives you have for an array, how many logical drives you have for an array.

Each physical drive has a spindle. When talking about the performance counter, there should not be more than 2 requests waiting in the queue at a time for a physical/logical drive. I am not sure about the calculation you mentioned.

-Keshav

 

[kmkeshav]

This link gives you a fair idea about performace counters for disk I/O in Windows 2000:

http://www.microsoft.com/technet/prodtechnol/Windows2000Pro/reskit/part6/proch30.mspx?mfr=true

This link gives you a fair idea about the physical contruction of a hard drive:

http://www.storagereview.com/guide2000/ref/hdd/op/index.html

 

[ericnet]

I see in the first link, the PhysicalDisk\Avg. Disk Queue Length performance counter threshold, in the description says “If more than two requests are continuously waiting on a single-disk system, the disk might be a bottleneck.”. So, I see that it refers to a normal hard disk (like in a normal PC are), which I suppose consists only in one physical disk, or something like that.. So, the performance counter value mentioned, if it is more than 3 (1 hard disk + 2) it can exist a bottleneck. This is what I didn’ t understand.

In PhysicalDisk\Avg. Disk Read Queue Length and PhysicalDisk\Avg. Disk Write Queue Length performance counters, that maximum value is 2 instead of 3. Correct?

 

[kmkeshav]

You are right as per Microsoft's documentation. There should not be more than 2 requests pending at a time for this counter.

-Keshav

 

[ericnet]

You said "There should not be more than 2 requests pending at a time for this counter.", then I am not correct.. Look at this article

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnpag/html/scalenetchapt15.asp

in the contents section clik on 'System Resources', and then scroll down until 'Disk I/O' section, and here read the first counter described which is we are talking. As you see, it says:
...
To measure disk I/O activity, you can use the following counters:

PhysicalDisk\Avg. Disk Queue Length
Threshold: Should not be higher than the number of spindles plus two.

Significance: This counter indicates the average number of both read and writes requests that were queued for the selected disk during the sample interval.

...

This means that there should not be more than 2 requests pending at a time?

 

[kmkeshav]

As for as the knowledge I gathered regarding Disk performance monitoring, some sources (including Microsoft link I provided)say value for this counter should not be more than 2. But the link you provided have a different value mentioned. Some sources say it can be up to 3 (Microsoft link you provided says the same). Practically I think we can have any value below or equal to 3 but not more than that.

If you look at the spindle calculation, a physical disk will have a single spindle and gives a value of 3 for this performance counter (no. of spindles + 2).

-Keshav

 

[ericnet]

Ok I see.., thank you very much for your help