Users Guide

There are limitations on the number of physical disks that can be included in the virtual disk. These limitations depend on the controller. When creating a
virtual disk, controllers support a certain number of stripes and spans (methods for combining the storage on physical disks). Because the number of total
stripes and spans is limited, the number of physical disks that can be used is also limited. The limitations on stripes and spans affect the possibilities for
concatenation and RAID levels as follows:
l Maximum number of spans affects concatenation, RAID 10, RAID 50, and RAID 60.
l Maximum number of stripes affects RAID 0, RAID 5, RAID 50, RAID 6, and RAID 60.
l Number of physical disks in a mirror is always 2. This affects RAID 1 and RAID 10.
In the case of RAID 50 and RAID 60, you can use a greater number of physical disks than is possible for the other RAID levels. RAID 10 on a SAS controller with
firmware version 6.1 can use a maximum of 256 physical disks. However, the number of connectors on the controller imposes limitations on how many physical
disks can be included in a virtual disk when using RAID 10, RAID 50, or RAID 60. This is because only a limited number of physical disks can be physically
attached to the controller.
For information on how many physical disks a controller supports per virtual disk, see the virtual disk specifications for the controller in "Supported Features."
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Maximum Number of Virtual Disks per Controller
Controllers have limitations on how many virtual disks can be created on the controller. For information on how many virtual disks the controller supports, see
the virtual disk specifications for the controller in "Supported Features."
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Calculation for Maximum Virtual Disk Size and the Create Virtual Disk Express Wizard
The Create Virtual Disk Express Wizard displays the minimum and maximum values for the virtual disk size. This section describes how the maximum possible
size for the virtual disk is calculated based on the controller type. To identify the controller type, see "RAID Controller Technology: SCSI, SATA, ATA, and SAS."
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SCSI, CERC SATA, and CERC ATA RAID Controllers
When using a SCSI, CERC SATA, or CERC ATA RAID controller, the controller calculates a maximum virtual disk size based on your RAID level selection and the
available physical disk space provided by all suitable physical disks attached to the controller. For example, if the controller contains 12 physical disks with
available space and you have specified a RAID 5, then the controller calculates the maximum virtual disk size based on the disk space provided by all 12
physical disks, because all 12 physical disks can be included in a RAID 5.
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SAS RAID Controllers
When using a SAS controller, the controller calculates the maximum virtual disk size based on the available disk space provided by the minimum number of
physical disks required to create the RAID level you selected. For example, if you specified a RAID 5, then the controller calculates the maximum virtual disk size
based on three physical disks, because only three physical disks are required to create a RAID 5.
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Channel Redundant Virtual Disks
When creating a virtual disk, it is possible to use disks attached to different channels to implement channel redundancy. This configuration might be used for
disks that reside in enclosures subject to thermal shutdown. See the following for more information:
l "SMART Thermal Shutdown"
l "Channel Redundancy and Thermal Shutdown"
Creating Virtual Disks
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Does my controller support this feature? See "Supported Features."
In order to implement RAID functions, you need to create a virtual disk. A virtual disk refers to storage created by a RAID controller from one or more physical
disks. Although a virtual disk may be created from several physical disks, it is seen by the operating system as a single disk. See "What Is RAID?" for more
information.
Before creating a virtual disk, you should be familiar with the information in "Considerations Before Creating Virtual Disks."
Storage Management provides wizards to help you create a virtual disk:
l The Create Virtual Disk Express Wizard calculates an appropriate virtual disk layout based on the available space and controller considerations. Using
the Express Wizard, you can quickly create a virtual disk using recommended selections. See "Create Virtual Disk Express Wizard (Step 1 of 2)" for more
information.
l The Create Virtual Disk Advanced Wizard allows you to specify the read, write, and cache policy for the virtual disk. You can also select the physical
disks and the controller connector to be used. You need a good knowledge of RAID levels and hardware to use the Advanced Wizard. See "Create
Virtual Disk Advanced Wizard (Step 1 of 4)" for more information.
NOTE: Channel redundancy only applies to controllers that have more than one channel and that attach to an external disk enclosure.