Storage Management Day-To-Day - Red Hat ENTERPRISE LINUX 4 - INTRODUCTION TO SYSTEM ADMINISTRATION Administration Manual

Chapter 5. Managing Storage
This makes it possible for a system administrator to treat all storage as being part of a single pool,
available for use in any amount. In addition, drives can be added to the pool at a later time, making it
a straightforward process to stay ahead of your users' demand for storage.
5.6.3.2. Logical Volume Resizing
The feature that most system administrators appreciate about LVM is its ability to easily direct storage
where it is needed. In a non-LVM system configuration, running out of space means — at best —
moving files from the full device to one with available space. Often it can mean actual reconfiguration
of your system's mass storage devices; a task that would have to take place after normal business
hours.
However, LVM makes it possible to easily increase the size of a logical volume. Assume for a moment
that our 200GB storage pool was used to create a 150GB logical volume, with the remaining 50GB
held in reserve. If the 150GB logical volume became full, LVM makes it possible to increase its size
(say, by 10GB) without any physical reconfiguration. Depending on the operating system environ-
ment, it may be possible to do this dynamically or it might require a short amount of downtime to
actually perform the resizing.
5.6.3.3. Data Migration
Most seasoned system administrators would be impressed by LVM capabilities so far, but they would
also be asking themselves this question:
What happens if one of the drives making up a logical volume starts to fail?
The good news is that most LVM implementations include the ability to migrate data off of a particular
physical drive. For this to work, there must be sufficient reserve capacity left to absorb the loss of the
failing drive. Once the migration is complete, the failing drive can then be replaced and added back
into the available storage pool.
5.6.3.4. With LVM, Why Use RAID?
Given that LVM has some features similar to RAID (the ability to dynamically replace failing drives,
for instance), and some features providing capabilities that cannot be matched by most RAID im-
plementations (such as the ability to dynamically add more storage to a central storage pool), many
people wonder whether RAID is no longer important.
Nothing could be further from the truth. RAID and LVM are complementary technologies that can be
used together (in a manner similar to nested RAID levels), making it possible to get the best of both
worlds.

5.7. Storage Management Day-to-Day

System administrators must pay attention to storage in the course of their day-to-day routine. There
are various issues that should be kept in mind:
Monitoring free space
•
Disk quota issues
•
File-related issues
•
Directory-related issues
•
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