■ Choose Automatic to allocate the disk to the pool and make it available for use as needed.
■ Choose Manual to allocate the disk to the pool but not allow it to be used until it is manually allocated.
■ Choose Hot Spare to allocate the disk to the pool as a spare disk that is made available for use if another disk in the pool fails or is removed from the subsystem.
5. When you are ready to continue, click Next. After you confirm your selections, click Create. The wizard tracks the progress of the pool creation. When the wizard finishes creating the pool, the View Results page will be updated to reflect this. Review the details to ensure that all phases were completed successfully, and then click Close.
■ If any portion of the configuration failed, note the reason for the failure and take corrective actions as appropriate before repeating this procedure.
■ If one of the physical disks is currently formatted with a volume, you’ll get the following error:
Could not create storage pool. One of the physical disks specified is not supported by this operation.
This error occurs because physical disks that you want to add to a storage pool cannot contain existing volumes. To resolve the problem, you’ll need to repeat the procedure and select a different physical disk, or remove any existing volumes on the physical disk, repeat the procedure, and then select the disk again. Keep in mind that deleting a volume permanently erases all data it contains.
■ If one of the physical disks is unavailable after being select, you’ll get the error:
Could not create storage pool. One or more parameter values passed to the method were invalid.
This error occurs because a physical disk that was available when you started the New Storage Pool Wizard has become unavailable or is offline. To resolve the problem, you’ll need to a) repeat the procedure and select a different physical disk, or b) bring the physical disk online or otherwise make it available for use, repeat the procedure, and then select the disk again.
NOTE external storage can become unavailable for a variety of reasons. For example, an external connected cable might have been disconnected or a LUN previously allocated to the server might have been reallocated by a storage administrator.
Creating a virtual disk in a storage space
After you create a storage pool, you can allocate space from the pool to virtual disks that are available to your servers. Each physical disk allocated to the pool can be handled in one of three ways:
■ As a data store that is available for use
■ As a data store that can be manually allocated for use
■ As a hot spare in case a disk in the pool fails or is removed from the subsystem
When a storage pool has a single disk, your only option for allocating space on that disk is to create virtual disks with a simple layout. A simple layout does not protect against disk failure. If a storage pool has multiple disks, you have these additional layout options:
■ Mirror With a mirror layout, data is duplicated on disks by using a mirroring technique similar to what I discussed previously in this chapter. However, the mirroring technique is more sophisticated in that data is mirrored onto two or three disks at a time. Like standard mirroring, this approach has its advantages and disadvantages. If a storage space has two or three disks, you are fully protected against a single disk failure, and if a storage space has five or more disks, you are fully protected against two simultaneous disk failures. The disadvantage is that mirroring reduces capacity by up to 50 percent. For example, if you mirror two 1-TB disks, the usable space is 1 TB.
■ Parity With a parity layout, data and parity information are striped across physical disks by using a striping-with-parity technique similar to what I discussed previously in this chapter. Like standard striping with parity, this approach has its advantages and disadvantages. You need at least three disks to fully protect yourself against a single disk failure. You lose some capacity to the striping, but not as much as with mirroring.
You can create a virtual disk in a storage pool by completing the following steps:
1. In Server Manager, select the File And Storage Services node, and then select the related Storage Pools subnode.
2. Select Tasks in the Virtual Disks panel, and then select New Virtual Disk. This starts the New Virtual Disk Wizard.
3. On the Storage Pool page, select the storage pool in which you want to create the virtual disk, and then click Next. Each available storage pool is listed according to the server it is managed by and available to. Make sure the pool has enough free space to create the virtual disk.
TIP Select the storage pool for the server you want to associate the virtual disk with and allocate storage from. For example, if you are configuring storage for CorpServer38, select a storage pool that is available to CorpServer38.
4. On the Specify The Virtual Disk Name page, enter a name and description for the virtual disk. If you are using a combination of SSD storage and HDD storage, use the check box provided to specify whether you want to create storage tiers. With storage tiers, the most frequently accessed files are automatically moved from slower HDD to faster SSD storage. This option is not applicable when the server has only HDD or SSD storage. To continue, click Next.
5. On the Select The Storage Layout page, select the storage layout as appropriate for your reliability and redundancy requirements. The simple layout is the only option for storage pools that contain a single disk. If the underlying storage pool has multiple disks, you can choose a simple layout, a mirror layout, or a parity layout. Click Next.
REAL WORLD If there aren’t enough available disks to implement the storage layout, you’ll get the error: The storage pool does not contain enough physical disks to support the selected storage layout. Select a different layout or repeat this procedure and select a different storage pool to work with initially.
■ Keep in mind the storage pool might have one or more disks allocated as hot spares. hot spares are made available automatically to recover from disk failure when you use mirroring or parity volumes-and cannot otherwise be used. To force Windows to use a hot spare, you can remove the hot spare from the storage pool by pressing and holding or right-clicking it and selecting Remove, and then adding the drive back to the storage pool as an automatically allocated disk by pressing and holding or right-clicking the storage pool and selecting Add Physical Drive. Unfortunately, doing so might cause a storage pool created with a hot spare to report that it is in an Unhealthy state. If you subsequently try to add the drive again in any capacity, you’ll get an error stating “Error adding task: The storage pool could not complete the operation because its configuration is read-only.” The storage pool is not, in fact, in a read-only state. If the storage pool were in a read-only state you could enter the following command at an elevated Windows PowerShell prompt to clear this state: