FAQ
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
(Work) 614-677-1668
(Cell) 614-312-6715

From:
"Herring Dave - dherri"
To:
"Oracle-L Freelists"
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
"Total in to be Moved Work" -
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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