Adding disks

Considerations when adding disks to a storage system  

The number of disks that are initially configured in RAID groups affects read and write performance. A greater number of disks means a greater number of independently seeking disk-drive heads reading data, which improves performance. Write performance can also benefit from more disks; however, the difference can be masked by the effect of nonvolatile RAM (NVRAM) and the manner in which WAFL manages write operations.

As more disks are configured, the performance increase levels off. Performance is affected more with each new disk you add until the striping across all the disks levels out. When the striping levels out, there is an increase in the number of operations per second and a reduced response time.

For overall improved performance, add enough disks for a complete RAID group. The default RAID group size is storage system-specific.

When you add disks to a storage system that is a target in a SAN environment, you should also perform a full reallocation scan. For more information, see your Block Access Management Guide.

Reasons to add disks  

You add disks for the following reasons:

• You want to add storage capacity to the storage system to meet current or future storage requirements
• You are running out of hot spare disks
• You want to replace one or more disks

Meeting storage requirements

To meet current storage requirements, add disks before a file system is 80 percent to 90 percent full.

To meet future storage requirements, add disks before the applied load places stress on the existing array of disks, even though adding more disks at this time will not significantly improve the storage system's current performance immediately.

Running out of hot spare disks

You should periodically check the number of hot spares you have in your storage system. If there are none, then add disks to the disk shelves so they become available as hot spares. For more information, see Hot spare disks.

Replacing one or more disks

You might want to replace a disk because it has failed or has been put out-of-service. You might also want to replace a number of disks with ones that have more capacity or have a higher RPM.

Prerequisites for adding new disks  

Before adding new disks to the storage system, be sure that the storage system supports the type of disk you want to add. For the latest information on supported disk drives, see the Data ONTAP Release Notes and the System Configuration Guide on the NOW site (http://now.netapp.com/).

Note
You should always add disks of the same size, the same checksum type, preferably block checksum, and the same RPM.

How Data ONTAP recognizes new disks  

When the disks are installed, they become hot-swappable spare disks, which means they can be replaced while the storage system and shelves remain powered on.

Once the disks are recognized by Data ONTAP, you, or Data ONTAP, can add the disks to a RAID group in an aggregate with the aggr add command. For backward compatibility, you can also use the vol add command to add disks to the RAID group in the aggregate that contains a traditional volume.

Physically adding disks to the storage system  

When you add disks to a storage system, you need to insert them in a disk shelf according to the instructions in the disk shelf manufacturer's documentation or the disk shelf guide provided by NetApp. For detailed instructions about adding disks or determining the location of a disk in a disk shelf, see your disk shelf documentation or the hardware and service guide for your storage system.

To add new disks to the storage system, complete the following steps.

aggr status -s

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Last updated: 01-Dec-2005 16:51:24