Tips and examples on allocating capacity

The physical disks in your provide the physical storage capacity for your data. Before you can begin storing data, you must configure the physical capacity into logical components known as and . These components are the tools that you use to configure, store, maintain, and preserve data on your storage array.

A disk group is a set of physical disks that the logically groups together to provide one or more virtual disks to an application . When you create a virtual disk from you can create a disk group and the virtual disk at the same time. When you create a virtual disk from you are creating an additional virtual disk on an already existing disk group.

When the advent of higher capacity physical disks and the ability to distribute virtual disks across RAID controller modules, creating more than one virtual disk per disk group is a good way to make use of your storage capacity and protect your data.

Tips for Allocating Capacity

Use the following tips to help guide you when configuring your storage array capacity:

When configuring the capacity on your storage array, make sure that you leave some unconfigured capacity remaining in the form of . This action enables you to have enough capacity available should you decide to create or .
A limit on the number of physical disks that you can assign to a disk group exists and is based on your total number of physical disks. If you attempt to overallocate the number of unassigned physical disks, you will be prompted by the storage management software to reduce the number of physical disks per disk group you are attempting to create or increase the number of disk groups being created.
Mixing different within a single disk group or virtual disk is not permitted.
Your host's operating system might have specific limits on how many virtual disks it can access. Consider these limits when creating virtual disks for use by a particular host. For information about host limitations, refer to the Storage System Product Release Notes.

Examples of Allocating Capacity

The following examples illustrate how altering your configuration choices affects the of your data.

Example 1 - No Enclosure Loss Protection

As the system administrator, you must manage a storage array consisting of eight expansion enclosures: the first five expansion enclosures contain physical disks, and the remaining three expansion enclosures contain SATA physical disks. Each expansion enclosure consists of 14 physical disks.

To accommodate your storage requirements, you must configure your storage array so that disk groups containing multiple virtual disks are created for your key business departments (IT, Marketing, and Finance). You have decided to use the SATA physical disks to configure the disk groups for IT and Finance and the Fibre Channel physical disks to configure the disk groups for the Marketing department.

Because you also plan to use snapshot virtual disks in the future, you must ensure that there is some unconfigured capacity remaining in the form of unassigned physical disks. The unconfigured capacity will be used to create to store snapshot-related information.

Use the following configuration options to achieve the storage requirements for this example:

1	Select for your RAID level.
2	Create a new disk group for each of your key business departments. When selecting the physical disks that will comprise the disk group, select multiple physical disks within the same expansion enclosure.
3	Confirm that you have unconfigured capacity available for future virtual disk requirements.

Because there is no enclosure loss protection and no have been assigned for the defined disk groups, you lose accessibility to the data on your disk group if there is a total loss of communication with a single expansion enclosure (such as a loss of power to the expansion enclosure or failure of both ).

Example 2 - Enclosure Loss Protection

As the system administrator, you must manage a storage array consisting of eight expansion enclosures: the first five expansion enclosures contain Fibre Channel physical disks, and the remaining three expansion enclosures contain SATA physical disks. Each expansion enclosure consists of 14 physical disks.

To accommodate your storage requirements, you must configure your storage array so that disk groups containing multiple virtual disks are created for your key business departments (IT, Marketing, and Finance). You also need to ensure that enclosure loss protection is achieved. You have decided to use the Fibre Channel physical disks to configure the disk groups for IT and Finance, and the SATA physical disks to configure the disk groups for the Marketing department.

Use the following configuration options to achieve the storage requirements for this example:

1	Select as the RAID level for your disk group.
2	Create a new disk group for each of your key business departments. When you select the physical disks that will comprise the disk group, ensure that each physical disk is located in a different expansion enclosures. This action achieves enclosure loss protection for the disk group. Tip: Choosing a suggested configuration in the Automatic Configuration Wizard: Choose Configuration dialog, or the Automatic option in the Create Virtual Disk Wizard: Specify Disk Group dialog makes achieving enclosure loss protection easier.
3	Select one hot spare physical disk per expansion enclosure to ensure maximum protection.
4	Confirm that you have unconfigured capacity available for future virtual disk requirements.

Using these configuration options, enclosure loss protection has been achieved for the defined disk groups. Even if a total loss of communication with a single expansion enclosure occurs, you still have access to the data on your disk groups.