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3ware® User Guide > Configuring Units > Configuring a New Unit > Configuration Options When Creating a Unit

Configuration Options When Creating a Unit
This section provides an overview of the choices you have when configuring a new unit. For step-by-step instructions, see Creating a Unit through 3DM and Creating a Unit through 3BM.
When you configure a new unit, you specify the following:
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Boot volume size (optional; can only be specified in 3BM or CLI)
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Multiple Volumes (optional; can only be specified in CLI)
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Unit policies that affect how the unit will be handled
You can make some types of changes to the RAID configuration later, and you can change the unit name and the unit policies. For details, see Changing An Existing Configuration by Migrating and Setting Unit Policies.
 
Note: If you will install the operating system on and boot from a unit managed through the new 3ware RAID controller, see First-Time RAID Configuration Using 3BM.
Drives to be included in the unit
You may include from one to thirty-two drives in the unit, depending on the number of drives available and the model of the controller you have. (For information about how many drives to select for a given RAID level, see Determining What RAID Level to Use.)
When creating units on the 9690SA controller, you cannot mix SAS and SATA drives in the same unit.
Available drives are those that are not currently part of a unit. If you want to use drives that are currently part of a different unit, you must first delete that unit to make the drives available. (For details, see Deleting a Unit.) If drives are listed under “Incomplete Drives and Others,” they must be deleted before they can be used.
If you want to add drives to a unit, see Adding a Drive.
Name of the unit (optional)
Units can be given names for easier identification. These names will be visible in 3DM, CLI, and 3BM.
Type of configuration (RAID Level)
Available configuration types include RAID 0, RAID 1, RAID 5, RAID 6, RAID 10, RAID 50, and Single Disk. For information about the different RAID levels, see Understanding RAID Concepts and Levels
 
Warning: Creating a unit writes the DCB and makes any earlier data on the drives inaccessible.
Stripe size, if appropriate for the RAID level
In general, smaller stripe sizes are better for sequential I/O, such as video, and larger stripe sizes are better for random I/O (such as databases).
Striping size is not applicable for RAID 1, because it is a mirrored array without striping.
Using the default stripe size of 64KB usually gives you the best performance for mixed I/Os. If your application has some specific I/O pattern (purely sequential or purely random), you might want to experiment with a smaller or larger stripe size.
Boot volume size
When you create a unit through 3BM or CLI, you can create a special volume to function as the boot volume. This is useful if you will be installing an operating system onto the unit, and want it to be installed in one volume and have a separate volume for data.
This is an optional feature. You do not have to create a boot volume if you plan to install the operating system on the unit.
If you are creating a very large unit and have enabled the Auto-Carving policy, the boot volume will be created in addition to any volumes created through auto-carving. For more information about auto-carving, see Using Auto-Carving for Multi LUN Support.
This feature can only be specified in 3BM and CLI.
Multiple Volumes
When you create a unit through CLI, you have the option of creating up to four volumes with variable, defined sizes. If you have enabled the Auto-Carving policy, these units will be created first, and then the carve size will be used to segment the remaining drive space into additional volumes. For details, see the /cx add command in the 3ware SAS/SATA RAID Controller CLI Guide.
Initialization Method
In 3BM, you can choose to do a foreground (default) or background initialization of the unit. 3DM and CLI can only use background initialization when creating a unit.
A foreground initialization will take place before the system is booted. It can take up to several hours, depending on the size of the unit.
A background initialization allows you to have immediate use of the unit, but will take longer and slows down performance of the unit until it completes.
If your unit starts a foreground initialization and you want to use it immediately, you can press Esc and the unit will switch to using background initialization.
Unit policies
Several unit policies are set when you create a new unit:
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The particular policies that you can adjust when you create the unit vary, depending on which program you are using: 3DM, 3BM, or the CLI.
You can change all of these policies after the unit has been created, with one exception. If Rapid RAID Recovery is disabled, it cannot be enabled later.
For a summary of what these policies do, see the discussion under Setting Unit Policies. For how to adjust each one, see the procedures later in this chapter.

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