Promise Technology UltraTrak100 TX8 - Manual (Page 16)

UltraTrak100 TX4 and UltraTrak100 TX8
User Manual
10
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.
C HOOSING S TRIPE B LOCK S IZE
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.
C HOOSING A RAID L EVEL
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
broken down into blocks and each block is
written to a separate disk drive
I/O performance is greatly improved by
spreading the I/O load across many
channels and drives
No parity calculation overhead is involved
Not a "True" RAID because it is not fault-
tolerant
The failure of just one drive will result in all
data in an array being lost
Should not be used in mission critical
environments
Recommended Applications for RAID 0
•
Image Editing
•
Pre-Press Applications
•
Any application requiring high bandwidth
RAID 1
Advantages Disadvantages
Simplest RAID storage subsystem design
Can increase read performance by
processing data requests in parallel since
the same data resides on two different
drives
High disk overhead - uses only 50% of
total capacity