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How to get ASM disk list on any DB instance that uses an ASM instance [message #499804] Wed, 16 March 2011 04:53 Go to next message
Michel Cadot
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My context on our servers is the following one:
- one ASM instance
- X DB instances
- each DB instance uses 2 or more dedicated diskgroups from the ASM instance
- there is one diskgroup named FREEDISK that contains spare disks

On each DB instance you can see:
- the list and global parameters of all diskgroups using v$asm_diskgroup view
- the list and parameters of all disks the instance is using with v$asm_disk view

So my question is: how (if this is possible) to know the list of (spare) disks in FREEDISK diskgroup?

Regards
Michel

Edit: I use 10.2 but if you have an answer for another version, it will be welcome.

[Updated on: Wed, 16 March 2011 04:54]

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Re: How to get ASM disk list on any DB instance that uses an ASM instance [message #499810 is a reply to message #499804] Wed, 16 March 2011 05:07 Go to previous messageGo to next message
ramoradba
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 select path
 from v$asm_disk
 where group_number in (select group_number from v$asm_diskgroup where name='FREEDISK');


Am I missing something here ?

Sriram

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Re: How to get ASM disk list on any DB instance that uses an ASM instance [message #499836 is a reply to message #499810] Wed, 16 March 2011 06:43 Go to previous messageGo to next message
Michel Cadot
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Yes, v$asm_disk contains ONLY disks you use in the DB instance you are.
In this case, FREEDISK contains disks that are not used (this is its purpose), so you don't see its disks in v$asm_disk.

Regards
Michel

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Re: How to get ASM disk list on any DB instance that uses an ASM instance [message #499849 is a reply to message #499836] Wed, 16 March 2011 07:55 Go to previous messageGo to next message
John Watson
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I think you have an architectural issue.
The RDBMS instance does not know which ASM instance is managing any particular disc group until it tries to use a file on the disc group, at which point it will ask the CSSD for the SID of the appropriate ASM instance. Then it can log on, and ask the ASM instance for the details of the group. So if you haven't used a file in the group, that connection hasn't been made.
A technology limitation!

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Re: How to get ASM disk list on any DB instance that uses an ASM instance [message #499865 is a reply to message #499849] Wed, 16 March 2011 08:50 Go to previous messageGo to next message
Michel Cadot
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In this point of view, yes, but any instance can see all diskgroups so why not all disks.
I don't think there is a technology limitation, maybe just an implementation one.
As you said, when an instance needs to use space on a diskgroup, it asks CSSD... but why couldn't it do it when it does not need to use space just wants to get these information?

Regards
Michel

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Re: How to get ASM disk list on any DB instance that uses an ASM instance [message #499874 is a reply to message #499865] Wed, 16 March 2011 09:12 Go to previous messageGo to next message
John Watson
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You could be right. The question of whether it is a technology limit or an implementation limit will depend on from where the RDBMS instance is getting the list of disc groups. If the list is provided by the CSSD, then we have a technology limit. If it provided by the ASM instance, we have an implemention limit.

There is a test that you can do on 10g. You can start two ASM instances, and give them each a different set of discs and disc groups. Then from your RDBMS instance, use files in only one disc group, and see if all disc groups across both ASMs are visible. That should determine where the list of groups is coming from, and thius where the limitation is.

I can't do this on my 11.2, because 11.2 permits only one ASM instance per node.

The test would be a lot of work, for (I think) purely academic interest. I love it.

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Re: How to get ASM disk list on any DB instance that uses an ASM instance [message #499879 is a reply to message #499874] Wed, 16 March 2011 09:21 Go to previous message
Michel Cadot
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Unfortunatly I have no test server to do this test but will try it one of my old laptops (the current one also ahs 11.2) as soon as possible (which will surely not be in the next few days).

Regards
Michel

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