Specifications
SCSI to SATA RAID Subsystem | Administrator’s Manual RAID Planning | en 23
Bosch Security Systems F.01U.027.802 | V1 | 2006.11
2 RAID Planning
This chapter summarizes the RAID configuration procedures and provides some useful tools
for first-time configuration.
2.1 Considerations
By the time you understand the basic ideas behind RAID levels, you may still be wondering
how to begin. Here are the answers to some questions that may help you through the decision
making process.
2.1.1 How many physical drives do you have?
When initially creating the drive groups, you should know how many drives you have in your
RAID system and in the expansion enclosure(s) or JBOD(s) attached to the RAID controlling
unit.
2.1.2 Limitations? Does my OS or HBA support 64-bit LBA?
A maximum of 64TB capacity can be included in a single logical drive.
If you have a picture of large arrays in mind, make sure both your host OS and HBA support
64-bit LBA. Not all OSes and HBA cards support 64-bit LBA. Some OSes, such as SuSE Linux
9, Windows 2003, Linux kernel 2.6X, support the addressability. Your HBA must also support
this feature. Please refer to the documentation that came with your OS and HBA card to
ensure the support for this feature.
Up to 128 members can be included in each logical drive. However, extreme array sizes can
cause operational problems with system backup or management and should be avoided.
2.1.3 How many drives on each drive channel?
Optimal system planning is always a compromise between pros and cons. As a general rule,
the number of drives you should connect on each channel equals the data bus bandwidth
divided by the maximum transfer rate you can get from each of your hard drives. Knowing the
mechanical performance of your hard drives can also help to determine how many drives to
connect over a drive channel.
Always use fast and large drives of the same capacity to compose a logical array. A logical
drive composed of an adequate number of larger drives can be more efficient than a logical
drive comprised of many but smaller drives.
2.1.4 How many drives would you like to appear to the host computer?
You must decide what capacity will be included in a logical configuration of drives, be it a log-
ical drive, a logical volume, or a logical partition. A logical configuration of drives will appear to
the host as a single capacity volume.
You may compose a large logical volume consisting of drives on different drive channels/enclo-
sures, and have it divided into smaller partitions. These partitions are then associated with
host channel ID/LUNs. Each logical partition will appear as an independent capacity volume.
2.1.5 What kind of host application?
The frequency of read/write activities can vary from one host application to another. The
application can be a SQL server, Oracle server, Informix, or other database server of a transac-
tion-based nature. Applications like video playback and video post-production editing require
read/write activities of large files coming in a sequential order.
Choose an appropriate RAID level for what is the most important for a given application –
capacity, availability, or performance. Before creating your RAID, you need to choose an opti-