| PRIMECLUSTER Global Disk Services Configuration and Administration Guide 4.2 (Linux) |
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| Appendix A General Notes | > A.3 General Points |
Pay attention to the following guidelines when constructing mirroring configurations.
Connecting disks and lower level groups with the same available sizes to mirror group is recommended.
The available size of a mirror group (the capacity available as volume) is the same as the available size of the smallest disk or lower level group that is connected.
When connecting disks or lower level groups with different available sizes to a mirror group, you will only be able to use the capacity of the smallest disk or lower level group. For example, if a 4 GB disk and a 9 GB disk is connected to one mirror group, only 4 GB out of the 9 GB disk will be accessible.
Mirroring disks with similar performance specifications, or groups with the same configuration (including the performance specifications of disks that is connected to the group) is recommended.
When mirroring disks with different performance specifications such as revolution speed, the read performance becomes unbalanced and the write performance will depend on the slower disk performance.
The same applies when mirroring disks and groups, or when mirroring groups with different configuration.
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