EMC Symmetrix DMX-3, Product Manual

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212 EMC Symmetrix DMX-3 Product Guide
Data Integrity, Availability, and Protection
Note: The amount of recommended spares in a Symmetrix system is
calculated by the EMC ordering system.
Example:
A system is configured with the following:
• 300 73 GB 15K drives
• 100 146 GB 15K drives
• 250 300 GB 10K drives
Spares will be calculated as follows:
Rule 1 requires 6 spares:
2 73 GB 15K drives
2 146 GB 15K drives
2 300 GB 10K drives
6 total spare drives
Since there is a total of 650 drives in the frame, rule 2 requires a
minimum of 9 spares, (2 base plus 7 for the 650 drives) Thus an
additional 3 drives, of the 300 GB 10K type must be added to reach a
total of 9.
This results in the following:
2 73 GB 15K drives
2 146 GB 15K drives
5 300 GB 10K drives
9 total spare drives
Note: These calculations are for the minimum number of spare drives. It is
usually a good idea to configure more than the minimum of two drives per
type to increase the likelihood that a permanent spare drive is always
available in a good location.
The EMC Customer Engineer can use Enginuity’s tools that define
and enforce the many complex sparing rules. One of these tools is a
disk map that shows each disk and the spares that cover it.
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When planning for spare drives, each of the system’s drive
capacity type, drive speed, and block sizes (512 or 520) must be
considered. A valid pool of spares for each type of failing drive
must be available.