T3 - How to create a mirror on a Sun StorEdge[TM] T3 array with an odd number of disks.

Asset ID:	1-71-1011897.1
Update Date:	2009-12-22
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Solution Type Technical Instruction Sure

Solution 1011897.1 : T3 - How to create a mirror on a Sun StorEdge[TM] T3 array with an odd number of disks.

Related Items


Sun Storage T3 Array

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GCS>Sun Microsystems>Storage - Disk>Modular Disk - Other

PreviouslyPublishedAs
216287

Description
T3 - How to create a mirror on a Sun StorEdge[TM] T3 array with an odd number of disks.

Steps to Follow
DESCRIPTION:

Creating a Raid-1 (mirror) out of an odd number of disks worked.

The T3 mirroring algorithm was written to accommodate mirrors with
odd-numbers of disks.   The intent of this document is to explain how
that works.
CREATING THE VOLUME:
Here is how one can create, via the CLI, a 3-disk RAID-1 (mirror).
Each of the disks used here are 18GB.
t3a:/:<10> vol add v1 data u1d1-3 raid 1
t3a:/:<11> vol init v1 data
WARNING - Volume data will be initialized to zero.
WARNING - Volume initialization can take a significant amount of time.
Continue   [N]: Y
t3a:/:<12> vol list
volume               capacity     raid     data         standby
v1                         26.8 GB       1         u1d1-3       none
Note that a 3-disk mirror of 18GB (actually 17.9GB) disks yields 26.8GB
of usable space.   That's 17.9GB times 3, then divided by 2 because the
data is mirrored.
17.9 x 3
--------   =   26.8
2
SO, HOW DOES THIS WORK    WHAT'S REALLY GOING ON
Assuming a 3-disk mirror, when one writes 6 blocks of data to the
mirror LUN, the 6 blocks (and likewise, subsequent blocks) will be
arranged on the 3 disks as shown below.   The "D" refers to data, and
the "M" refers to mirror.
With the data arranged in this fashion, it is easy to see that if a
disk fails, the data will still be available.
disk-1   disk-2   disk-3
+-------------------------
Data ->     |   blk1       blk2       blk3
Mirror -> |   blk3       blk1       blk2
Data ->     |   blk4       blk5       blk6
Mirror -> |   blk6       blk4       blk5

Product
Sun StorageTek T3 Array

Previously Published As
22450

Change History
Date: 2003-11-14
User Name: 81292
Action: Approved
Comment:
KCCP: OK to publish
Version: 0
Date: 2003-11-14
User Name: 38035
Action: Approved
Comment: reviewed as part of the KM&O KCCP project; content is valid
Version: 0
Date: 2003-11-04
User Name: 110334
Action: Rejected
Comment: I'm not questioning the accuracy of the doc. It seems to be a duplicate. See previous comments.
Version: 0
Product_uuid
2a6d7d50-0a18-11d6-8e0b-f0bd33b24928|Sun StorageTek T3 Array

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