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ASM Confusions [message #440760] Tue, 26 January 2010 23:10 Go to next message
bryanadams
Messages: 9
Registered: September 2009
Location: Bangalore
Junior Member
Hi,

I am working on ASM as i am bit confused to decide ASM Disk strategies in production Environments.

For Ex:-

1.Normal Redundancy ( Allows 2 Mirror Groups ) :-
I have created Normal_DG Diskgroup with 4 Disks
Disk1-------------------
Disk2 -------           |
             |--->FG2    ----> FG1
Disk3 -------           |
Disk4-------------------


According to my understanding , if Disk1 Fails Disk4 facilitates normal operations. When there is space crunch it operates in reduced redundancy . Am i right ?

2.I have got 4 Disks in one group (i.e from Disk1 To Disk4 ) i have not defined any failure group and as per my understanding all disks will be added to its own failure group without mirroring and striping. Am i right ?

Regards
Bryan.

[Updated on: Tue, 26 January 2010 23:26]

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Re: ASM Confusions [message #440808 is a reply to message #440760] Wed, 27 January 2010 02:19 Go to previous messageGo to next message
John Watson
Messages: 6403
Registered: January 2010
Location: Global Village
Senior Member
Hi - you have the wrong idea about failure groups: you are describing the opposite of the way they work. The documentation is clear: "Oracle ASM chooses the disk on which to store the secondary copy so that it is in a different failure group than the primary copy" (taken from the Storage Administrator's Guide).
I'm not sure whatyou mean by "space crunch", but the only circumstance in which thew redundancy will be reduced is if you lose a disk, so that mirroring is no longer possible.
Why would you say that with four discs in one group you will have neither striping nor mirroring? Does the explanation above help?
Re: ASM Confusions [message #440827 is a reply to message #440808] Wed, 27 January 2010 04:22 Go to previous message
bryanadams
Messages: 9
Registered: September 2009
Location: Bangalore
Junior Member
Hi,

I hope my question is clear .. but any way space crunch is something i mentioned due to

A normal redundancy disk group can tolerate the failure of one failure group. If only one failure group fails, the disk group remains mounted and serviceable, and ASM performs a rebalance of the surviving disks (including the surviving disks in the failed failure group) to restore redundancy for the data in the failed disks. If more than one failure group fails, ASM dismounts the disk group.

And for the second question ..

Mirroring of metadata and user data is achieved through failure groups. System reliability can be hampered if an insufficient number of failure groups are provided. Consequently, failure group configuration is very important to creating a highly reliable system.

Both the above text has been pasted from Oracle Administartion Guide http://download.oracle.com/docs/cd/B19306_01/server.102/b14231/storeman.htm#sthref1675

I am not able to understand this properly .. that is reason i have posted the question by showing the disks example

Regards

[Updated on: Wed, 27 January 2010 04:29]

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