24Understanding Veritas Volume Manager

How VxVM handles storage management

Figure 1-3

Example configuration for disk enclosures connected via a fibre

 

channel hub or switch

c1Host

Fibre Channel hub or switch

Disk enclosures

enc0

enc1

enc2

In such a configuration, enclosure-based naming can be used to refer to each disk within an enclosure. For example, the device names for the disks in enclosure enc0 are named enc0_0, enc0_1, and so on. The main benefit of this scheme is that it allows you to quickly determine where a disk is physically located in a large SAN configuration.

Note: In many advanced disk arrays, you can use hardware-based storage management to represent several physical disks as one logical disk device to the operating system. In such cases, VxVM also sees a single logical disk device rather than its component disks. For this reason, when reference is made to a disk within an enclosure, this disk may be either a physical or a logical device.

Another important benefit of enclosure-based naming is that it enables VxVM to avoid placing redundant copies of data in the same enclosure. This is a good thing to avoid as each enclosure can be considered to be a separate fault domain. For example, if a mirrored volume were configured only on the disks in enclosure enc1, the failure of the cable between the hub and the enclosure would make the entire volume unavailable.

If required, you can replace the default name that VxVM assigns to an enclosure with one that is more meaningful to your configuration. See “Renaming an enclosure” on page 155 for details.