Re: ASM rebalance estimates

From: <TESTAJ3_at_nationwide.com>
Date: Thu, 9 Sep 2010 11:54:54 -0400
Message-ID: <OFB55904C7.13032552-ON85257799.00574459-85257799.00576CD6_at_lnotes-gw.ent.nwie.net>



I think this going to me one of those "your mileage my vary" things.

even a guesstimate from my environment would have absolutely no bearing on your environment. speed of disks, amount of cpu already being used, etc.

I don't think you'll get a firm answer because there really isn't one.

joe



Joe Testa, Oracle Certified Professional Senior Engineering & Administration Lead (Work) 614-677-1668
(Cell) 614-312-6715

From:
"Herring Dave - dherri" <Dave.Herring_at_acxiom.com>
To:
"Oracle-L Freelists" <oracle-l_at_freelists.org>
Date:
09/09/2010 11:19 AM
Subject:
ASM rebalance estimates
Sent by:
oracle-l-bounce_at_freelists.org

Folks,

Has anyone done any detailed investigations on how to estimate the time needed for a disk add and rebalance operation with ASM? Athough everything can be done "hot", our client (like probably most) requires us to perform the adding of any disks to ASM during our maintenance window and also asks for an estimate on the time involved. Their expectation has been that the time involved is only affected by the # of disks added. My contention is it's that plus the amount of data to be rebalanced, basically existing disk fullness or size of the diskgroup.

Assuming everything stays consistent (power of 11 for the rebalance operation, load on the diskgroup, and each LUN or "disk" is physically made up of the same # and capacity of physical disks) here's what I believe to be true:

  • If you had 10 x 100 GB disks that were 80% full (or 800 GB of total data) and added 2 x 100 GB disks, the final set should be 12 x 100 GB disks with 800 GB of data balanced across them, so each would have 66.67 GB of data. To me that means, at a minimum, you'd have to move 10(80-66.67) = 133 GB of data.
  • Take the same scenario but this time the disks are 60% full (or 600 GB of total data), the final set should be 12 x 100 GB disks with 600 GB of data balanced across them, so each would have 50 GB of data. To me that means, at a minimum, you'd have to move 10(60-50) = 100 GB of data.

Unfortunately I don't have any system to test this on and existing data is way off from my assumption on what's being done. Here's a listing of what I've collected:

                                                                 Size of
                                                 # of            Disks    
# of                                                             Used GB   
Est. GB          GB                              "Total
                 Elapsed                 Disks           Added   Existing  
 "Total          in                              to be  Moved    Work" -
Server (Min.)            Added (GB)                              Disks    
Work"                            Diskgroup               Moved   per Min   
Est. Work
LnxA             412                             9               118   51  
                 1,763,618               5,747 862.05            2.09   
880,879
LnxB             228                             3               269   13  
                   534,693               2,814 527.63            2.31   
-5,595
LnxB             166                             4               118   51  
                   792,866               5,662 411.78            2.48   
371,201
LnxC             202                             4               118   51  
                 1,199,042               5,820 423.27            2.10   
765,611
LnxC             216                             7               118   46  
                   931,080               5,339 705.15            3.26   
209,005
LnxD             98                              3               118   11  
                   332,504               1,218 261.00            2.66   
65,240
LnxD             98                              1               118   10  
                   174,605               1,152 104.73            1.07   
67,364
LnxE             76                              3               118   11  
                   321,145               1,176 252.00            3.32   
63,097

"Total Work" refers to the column in V$ASM_OPERATION and the value listed
is the last one displayed from this view before the operation completed.

Has anyone done any research into this or recorded similar data?

Thx.

Dave Herring | DBA, Global Technology Services A c x i o m C o r p o r a t i o n
630-944-4762 office | 630-430-5988 cell | 630-944-4989 fax 1501 Opus Pl | Downers Grove, IL, 60515 | U.S.A. | www.acxiom.com Service Desk: 888-243-4566, https://servicedesk.acxiom.com, GSCA_at_DNB.com



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Received on Thu Sep 09 2010 - 10:54:54 CDT

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