Promise Technology TX8, TX4 user manual Choosing a RAID Level, Advantages Disadvantages

UltraTrak100 TX4 and UltraTrak100 TX8 User Manual

For the Gigabyte Boundary feature to work, the Gigabyte Boundary feature must be set to ON when the original array is created. When enabled, the Gigabyte Boundary feature rounds the drive capacity of all drives to the common whole GB drive size. For example, with the Gigabyte Boundary feature enabled, the remaining working drives can be 20.5 GB and the replacement drive can be 20.3, since all are rounded down to 20GB. This permits the smaller drive to be used. Please note that users will lose a small amount of available storage capacity from each drives in order to arrive at a common drive size.

CHOOSING STRIPE BLOCK SIZE

There are two issues to consider when selecting the Stripe Block Size.

First, you should choose a Stripe Block Size equal-to or smaller than the smallest cache buffer found on any array disk drive. Selecting a larger value slows the array down because disk drives with smaller cache buffers need more time for multiple accesses to fill their buffers.

Secondly, if your data retrieval consists of fixed data blocks, such as with some database or video applications – then you should choose that size as your Stripe Block Size.

CHOOSING A RAID LEVEL

There are several issues to consider when choosing the RAID Level for your UltraTrak100 array. Appendix A - Technology Background on page 41 gives some technical insight regarding each RAID choice and the following discussion summarizes some advantages, disadvantages and applications for each choice.

RAID 0

Advantages	Disadvantages
Implements a striped disk array, the data is	Not a "True" RAID because it is not fault-
broken down into blocks and each block is	tolerant
written to a separate disk drive	The failure of just one drive will result in all
I/O performance is greatly improved by	data in an array being lost
spreading the I/O load across many	Should not be used in mission critical
channels and drives
	environments
No parity calculation overhead is involved

Recommended Applications for RAID 0

•Image Editing

•Pre-Press Applications

•Any application requiring high bandwidth

RAID 1

Advantages	Disadvantages
Simplest RAID storage subsystem design	High disk overhead - uses only 50% of
Can increase read performance by	total capacity
processing data requests in parallel since
the same data resides on two different
drives

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