Mirroring Between Two Disks of Different Sizes

Troubleshooting

Problem

Starting with v5r4m0, IBM i OS mirrored protection has allowed for mirroring of drives that are not the exact same size.

Resolving The Problem

Starting with v5r4m0, IBM i OS mirrored protection has allowed for mirroring of drives that are not the exact same size. In order to allow mirroring between two drives of different sizes, the Free Space Map of the two drives must be the same size.

The following list shows the range of drive sizes (approximate value) that would have a Free Space Map of the same size:

8 GB < Unit Size <= 25 GB
25 GB < Unit Size <= 51 GB
51 GB < Unit Size <= 77 GB
77 GB < Unit Size <= 102 GB
102 GB < Unit Size <= 128 GB
128 GB < Unit Size <= 154 GB
154 GB < Unit Size <= 179 GB
179 GB < Unit Size <= 205 GB
205 GB < Unit Size <= 231 GB
231 GB < Unit Size <= 256 GB
256 GB < Unit Size <= 282 GB
282 GB < Unit Size <= 308 GB
308 GB < Unit Size <= 333 GB
333 GB < Unit Size <= 359 GB
359 GB < Unit Size <= 385 GB
385 GB < Unit Size <= 410 GB
410 GB < Unit Size <= 462 GB
462 GB < Unit Size <= 513 GB
513 GB < Unit Size <= 564 GB
564 GB < Unit Size <= 616 GB
616 GB < Unit Size <= 667 GB
667 GB < Unit Size <= 719 GB
719 GB < Unit Size <= 770 GB
770 GB < Unit Size <= 821 GB
821 GB < Unit Size <= 924 GB
924 GB < Unit Size <= 1027 GB (1 TB)
1027 GB < Unit Size <= 1129 GB (1.1 TB)
1129 GB < Unit Size <= 1232 GB (1.2 TB)
1232 GB < Unit Size <= 1438 GB (1.4 TB)
1438 GB < Unit Size <= 1643 GB (1.6 TB)
1643 GB < Unit Size <= 2054 GB (2.0 TB)
2054 GB < Unit Size <= 2465 GB (2.4 TB)
2465 GB < Unit Size <= 2876 GB (2.8 TB)
2876 GB < Unit Size <= 3287 GB (3.2 TB)
3287 GB < Unit Size <= 3697 GB (3.6 TB)
3697 GB < Unit Size <= 4108 GB (4.0 TB)
4108 GB < Unit Size <= 4519 GB (4.4 TB)
4519 GB < Unit Size <= 4930 GB (4.8 TB)

Note: When replacing a suspended unit, you can only replace it with a unit of the same size or larger, even if they have the same free space size.

For example, if you have a suspended mirror disk that is 950 GB, you can replace that suspended unit with a disk that is 1000 GB. However, if the suspended mirror disk unit was 1000 GB, you cannot replace that with a disk that is 950 GB.

Note: Mirroring is not supported between units using different sector formats.

For example, a 512 byte sector disk can not be mirrored to a 520, 4096 or 4160 byte sector disk. However you can mirror a 520 byte sector disk with a 4160 byte sector disk because the format is considered the same.

Note: Maximum disk size was increased from 2 TB to 4.8 TB in V7R2 TR7. Reference IBM Documentation Miscellaneous limits for Maximum disk size per OS version

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Historical Number

568335607

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Document Information

More support for:
IBM i

Component:
IBM i

Software version:
6.1.0, 7.1.0, 7.2.0, 7.3.0, 7.4.0, 7.5.0

Operating system(s):
IBM i

Document number:
686247

Modified date:
15 October 2024

UID

nas8N1012106

IBM Support

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