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Unix Backup and Recovery by W. Curtis Preston

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HA Building Blocks

Many people begin adding availability to their systems in levels. They start by increasing the availability of their disks by using volume management software to place their disks in some sort of RAID[42] configuration. They also begin increasing filesystem availability by using a journaling filesystem. Here is an overview of these concepts.

Volume Management

There are two ways to increase the availability of your disk drives. The first is to buy a hardware-based RAID box, and the second is to use volume management software to add RAID functionality to “regular” disks.

Tip

The storage industry uses the term “volume management” when talking about managing multiple disks, especially when striping or mirroring them with software. Please don’t confuse this with managing backup volumes (i.e., tapes, CDs, optical platters, etc.).

The amount of availability that you add will be based on the level of RAID that you choose. Common numbered examples of RAID are RAID-0, RAID-1, RAID-0+1, RAID-1+0, RAID-10 (1+0 and 10 refer to the same thing), RAID-2, RAID-3, RAID-4, RAID-5, and RAID-6. See Table 6-1 for a brief description of each RAID level. A more detailed description of each level follows.

Table 6-1. RAID Definitions

Level

Description

RAID:

A disk array in which part of the physical storage capacity is used to store redundant information about user data stored on the remainder of the storage capacity. The redundant information enables regeneration of user data in the ...

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