53
System Connection
This chapter outlines the general configuration rules you should follow when cabling
a storage system and introduces basic information about topologies. You can use
these topologies or refer to them as a guide for developing your own unique
topologies. A complete description of the power-on and power-off procedures is also
given in this chapter.
General Considerations on Making Connections
When selecting the number of hard drives to be included in a logical drive, the host
channel bandwidth and the mechanical performance of individual disk drives should
be considered.
It is a good practice to calculate performance against the host port bandwidth when
designing an application topology. As an example, if eight members are included in a
logical drive and this logical drive is associated with a host ID (LUN mapping), the
combined performance of this logical drive should approximate the channel
bandwidth. If, for example, two 6-drive logical arrays are associated with two IDs
residing on a single host channel, there may be a trade-off with performance.
If your system comes with a total of 8+ host ports, it is recommended that you obtain
more disk drives by attaching an expansion enclosure so that you can create
host-port corresponding 6-member logical drives (RAID-5) or 8-member logical
drives (RAID-6). These logical drives leverage the bandwidth of each host port.
There are other considerations:
For example, a spare drive carries no data stripes and will not contribute to
disk-level performance. Refer to the documentation for your hard drives for
performance data.
The disk drives in the same logical array should have the same capacity, but it
is preferred that all the drives within a chassis have the same capacity.
Disk drives in the same logical drive should have the same capacity, but it is
preferred that all the disk drives within a chassis have the same capacity. You
should not include both SAS and SATA drives in a logical drive.
A spare drive should have a minimum capacity that is equivalent to the largest
