3.2.1.1 Disk Level Logical Sets

With Disk Level logical sets, two or more entire disks are combined into one logical disk using a single RAID type. At the disk level, the RAIDZONE Administrator software supports only RAID 1 (mirroring). At the partition level, RAID levels 0 (striping), 1 (mirroring) and 5 (striping with striped parity) are supported. To implement RAID 10 (striped mirrors), you create one or more mirrored pairs at the disk level, then apply striping to them at the partition level.

Mirroring is a fault tolerant configuration that provides complete redundancy by writing identical copies of all data on a pair of disks. The overhead of performing duplicate writes is quite low, since the two disks can be written in parallel. In addition to fault tolerance, mirroring also provides improved read performance, because both drives can be read in parallel.

If you have decided to set up a mirrored pair of drives for RAID 0 or RAID 10, hold down the CTRL key while using the mouse to select the two drives that will be mirrored. Once you have the two drives highlighted, release the CTRL key and use the mouse to select Configure from the menu, then New Mirror. The following dialog box will appear:

Click the Yes button, and the mirrored pair will be set up for you. The screen will look like this:

In this example, we have a single RAIDZONE SmartCan enclosure containing five disks. The fourth and fifth disks have just been configured as a mirrored pair, but the mirror has not been initialized.

When a pair of disks is configured to be a mirrored set, RAIDZONE selects one of the disks as the "primary" disk and the other as the "secondary" disk. During initialization, the data on the primary disk will be copied to the secondary disk.

In general, if either disk has a valid existing partition that disk will be selected as the primary disk. This allows you to mirror a pre-existing disk. If both disks have valid partitions, RAIDZONE will require that the partitions on one of the disks be removed before establishing the mirror. If neither disk has any existing partitions, then RAIDZONE will select the disk with the lowest disk ID number as the primary disk.

Since the disks in a mirrored set are duplicates of each other, they must have the same physical disk size. However, they do not need to have the same disk geometry (i.e. the number of heads, cylinders and sectors).

In the above example, the fifth disk is labelled "Member 0", which indicates that it is the primary disk of the mirrored pair. Its icon is yellow because its state is healthy but its data is not redundant (since the mirror has not yet been initialized). The fourth disk is labelled "Member 1", which indicates that it is the secondary disk of the mirrored pair. Its icon is red because its data needs to be initialized or rebuilt.

After you have established a mirrored pair, initialization of the data is performed on the next reboot. After a system reboot, the secondary side of the mirrored set is hidden from the rest of the operating system. The RAIDZONE Administrator program displays both disks, using a common colored outline to couple the two disks in the set, but only the primary disk will have partition information displayed.

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