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<h1 class="topictitle1">Disk storage concepts</h1>
<div><p>Disk units are assigned to a disk pool on a storage unit basis. The system
treats each storage unit within a disk unit as a separate unit of auxiliary
storage. When a new disk unit is attached to the system, the system initially
treats each storage unit within it as nonconfigured. You can <a href="rzalyadd.htm">add</a> these nonconfigured storage units to either the system
disk pool, basic disk pool, or independent disk pool of your choosing. When
adding nonconfigured storage units, use the serial number information that
is assigned by the manufacturer to ensure that you are selecting the correct
physical storage unit. Additionally, the individual storage units within the
disk unit can be identified through the address information that can be obtained
from the DST Display Disk Configuration display.</p>
<p>When you add a nonconfigured storage unit to a disk pool, the system assigns
a unit number to the storage unit. The unit number can be used instead of
the serial number and address. The same unit number is used for a specific
storage unit even if you connect the disk unit to the system in a different
way.</p>
<p>When a unit has mirrored protection, the two storage units of the mirrored
pair are assigned the same unit number. The serial number and the address
distinguish between the two storage units in a mirrored pair.</p>
<p>To determine which physical disk unit is being identified with each unit
number, make note of the unit number assignment to ensure correct identification.
If a printer is available, print the display of your disk configuration. If
you need to verify the unit number assignment, use iSeries™ Navigator to display disk unit
properties and check the serial numbers and addresses of each unit.</p>
<p>The storage unit that is addressed by the system as unit 1 is always used
by the system to store licensed internal code and data areas. The amount of
storage that is used on unit 1 is quite large and varies depending on the
configuration of your system. Unit 1 contains a limited amount of user data.
Because unit 1 contains the initial programs and data that are used during
an IPL of the system, it is also known as the loadsource unit.</p>
<p>The system reserves a fixed amount of storage on units other than unit
1. The size of this reserved area is 1.08 MB per unit, reducing the space
available on each unit by that amount.</p>
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<div>
<ul class="ullinks">
<li class="ulchildlink"><strong><a href="rzalyxdskcfg.htm">Components of disk storage</a></strong><br />
</li>
<li class="ulchildlink"><strong><a href="rzalymultipath.htm">Considerations for multipath disk units</a></strong><br />
</li>
</ul>
<div class="familylinks">
<div class="parentlink"><strong>Parent topic:</strong> <a href="rzalydmconcepts.htm" title="Learn about how disk storage works, how you can leverage disk pools in your environment. Protect your data with device parity protection and mirrored protection.">Disk management concepts</a></div>
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