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Greg Rahn
http://structureddata.org
-------- Original Message --------
Subject: Re:ASM question
From: "Hameed, Amir" <Amir.Hameed_at_xerox.com>
To: "Greg Rahn" <greg_at_structureddata.org>
Date: 2/23/2007 1:15 PM
> Thank you for your explanation.
> Amir
>
> ------------------------------------------------------------------------
> *From:* Greg Rahn [mailto:greg_at_structureddata.org]
> *Sent:* Friday, February 23, 2007 3:17 PM
> *To:* Hameed, Amir
> *Subject:* Re: ASM question
>
> First, lets understand a couple things:
>
> ASM Failgroups & normal redundancy: Any ASM disk in a given
> failgroup may not have its extent mirrors on any other asm disk in
> that same failgroup.
> 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.
>
> |REQUIRED_MIRROR_FREE_MB| indicates the amount of space that must
> be available in the disk group to restore full redundancy after
> the worst failure that can be tolerated by the disk group.
>
> http://download-east.oracle.com/docs/cd/B19306_01/server.102/b14231/storeman.htm
>
> In your second example the 7627GB USABLE_FILE_MB comes from here:
> The worst failure that this disk group could tolerate is 1 ASM
> disk failure (this is where |REQUIRED_MIRROR_FREE_MB = 5GB comes
> from)| and still restore full redundancy. Given that, 100% of the
> data and its redundant copy would have to reside on 3 asm disks.
> So if ASM needs to support 4 ASM disks data on 3 ASM disks no more
> than 75% of the capacity could be used. Using normal redundancy
> the math would be:
> 4 ASM disks @5GB = 20GB = TOTAL_MB
> 20GB TOTAL_MB / 2 = 10GB (for primary extent mirrors)
> 3/4 (support 4 disks data on 3) * 10GB = 7.5GB
>
> In the first example |REQUIRED_MIRROR_FREE_MB is 0 because that
> diskgroup could not sustain a failure and still restore full
> redundancy.|
>
> Regards,
> -Greg
>
>
> -------- Original Message --------
> Subject: ASM question
> From: "Hameed, Amir" <Amir.Hameed_at_xerox.com>
> To: oracle-l_at_freelists.org
> Date: 2/23/2007 10:13 AM
>> Hi Folks,
>> I have a 10.2.0.2 ASM instance running on Solaris 9 with the following
>> scenario:
>>
>> 1. All raw disk slices are 5GB in size
>>
>> 2. I have created a normal redundancy ASM diskgroup with two failure
>> groups as shown below:
>> SQL> create diskgroup data normal redundancy
>> failgroup failgroup_1
>> disk '/dev/vx/rdsk/ux016_RAW/volraw_01'
>> failgroup failgroup_2
>> disk '/dev/vx/rdsk/ux016_RAW/volraw_02'
>> /
>>
>> When I run the sql statement, as shown below, I see the following
>> output:
>> SQL> select GROUP_NUMBER GROUP#, NAME, STATE, TOTAL_MB, FREE_MB,
>> REQUIRED_MIRROR_FREE_MB REQ_MIRR_FREE_MB, USABLE_FILE_MB
>> from V$ASM_DISKGROUP;
>>
>> GROUP# NAME STATE TOTAL_MB FREE_MB
>> REQ_MIRR_FREE_MB USABLE_FILE_MB
>> ---------- -------------- --------------- ---------- ----------
>> ---------------- --------------
>> 1 DATA MOUNTED 10240 10138
>> 0 5069
>>
>> So, the total size of the DG is 10GB with Usable space of 5GB. Because
>> the group is mirrored 1:1, the REQ_MIRR_FREE_MB is zero.
>>
>> 3. When I create the same group with two disks in each failover group, I
>> see an output that I am not able to comprehend:
>> SQL> create diskgroup data
>> failgroup failgroup_1
>> disk
>> '/dev/vx/rdsk/ux016_RAW/volraw_01',
>> '/dev/vx/rdsk/ux016_RAW/volraw_02'
>> failgroup failgroup_2
>> disk
>> '/dev/vx/rdsk/ux016_RAW/volraw_03',
>> '/dev/vx/rdsk/ux016_RAW/volraw_04'
>> /
>>
>> SQL> select GROUP_NUMBER GROUP#, NAME, STATE, TOTAL_MB, FREE_MB,
>> REQUIRED_MIRROR_FREE_MB REQ_MIRR_FREE_MB, USABLE_FILE_MB
>> from V$ASM_DISKGROUP;
>>
>> GROUP# NAME STATE TOTAL_MB FREE_MB
>> REQ_MIRR_FREE_MB USABLE_FILE_MB
>> ---------- -------------- --------------- ---------- ----------
>> ---------------- --------------
>> 1 DATA MOUNTED 20480 20374
>> 5120 7627
>>
>> I was hoping to see REQ_MIRR_FREE_MB of zero because I have a DG that
>> contains two failure groups with each group contains two disks. I was
>> also expecting to see 10GB for the USABLE_FILE_MB.
>>
>> Can someone please clarify how two interpret these stats.
>>
>> Thanks
>> Amir
>>
>> --
>> http://www.freelists.org/webpage/oracle-l
>>
>>
>>
>
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Received on Fri Feb 23 2007 - 18:29:10 CST
