Administrator Guide

Table 12. Drawer loss protection requirements for different raid levels (continued)
RAID Level Drawer Loss Protection Requirements
RAID Level 5 RAID Level 5 requires a minimum of 3 physical disks. Place all the physical disks in different drawers for a
RAID Level 5 disk group. Drawer loss protection cannot be achieved for RAID Level 5 if more than one
physical disk is placed in the same drawer.
RAID Level 1 and RAID Level
10
RAID Level 1 requires a minimum of 2 physical disks. Make sure that each physical disk in a remotely
replicated pair is located in a different drawer. By locating each physical disk in a different drawer, you can
have more than two physical disks of the disk group within the same drawer. For example, if you create a
RAID Level 1 disk group with six physical disks (three replicated pairs), you can achieve the drawer loss
protection for the disk group with only two drawers as shown in this example: 6-physical disk RAID Level 1
disk group:
Replicated pair 1 = Physical disk located in enclosure 1, drawer 0, slot 0, and physical disk in enclosure 0,
drawer 1, slot 0
Replicated pair 2 = Physical disk in enclosure 1, drawer 0, slot 1, and physical disk in enclosure 1, drawer 1,
slot 1
Replicated pair 3 = Physical disk in enclosure 1, drawer 0, slot 2, and physical disk in enclosure 2, drawer 1,
slot 2
RAID Level 10 requires a minimum of 4 physical disks. Make sure that each physical disk in a remotely
replicated pair is located in a different drawer.
RAID Level 0 You cannot achieve drawer loss protection because the RAID Level 0 disk group does not have
consistency.
NOTE: If you create a disk group using the Automatic physical disk selection method, MD Storage Manager attempts to
choose physical disks that provide drawer loss protection. If you create a disk group by using the Manual physical disk
selection method, you must use the criteria that are specified in the previous table.
If a disk group already has a Degraded status due to a failed physical disk when a drawer fails, drawer loss protection does not protect the
disk group. The data on the virtual disks becomes inaccessible.
Host-to-virtual disk mapping
After you create virtual disks, you must map them to the host(s) connected to the array.
The following are the guidelines to configure host-to-virtual disk mapping:
• Each virtual disk in the storage array can be mapped to only one host or host group.
• Host-to-virtual disk mappings are shared between controllers in the storage array.
• A unique LUN must be used by a host group or host to access a virtual disk.
• Each host has its own LUN address space. MD Storage Manager permits the same LUN to be used by different hosts or host groups
to access virtual disks in a storage array.
• All operating system do not have the same number of LUNs available.
• You can define the mappings on the Host Mappings tab in the AMW. See Using The Host Mappings Tab.
Creating host-to-virtual disk mappings
Guidelines to define the mappings:
• An access virtual disk mapping is not required for an out-of-band storage array. If your storage array is managed using an out-of-band
connection, and an access virtual disk mapping is assigned to the Default Group, an access virtual disk mapping is assigned to every
host created from the Default Group.
• Most hosts have 256 LUNs mapped per storage partition. The LUN numbering is from 0 through 255. If your operating system
restricts LUNs to 127, and you try to map a virtual disk to a LUN that is greater than or equal to 127, the host cannot access it.
• An initial mapping of the host group or host must be created using the Storage Partitioning Wizard before defining additional
mappings. See Storage Partitioning.
To create host to virtual disk mappings:
1. In the AMW, select the Host Mappings tab.
2. In the object tree, select:
Disk groups, standard virtual disks, and thin virtual disks
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