Choosing the Right Disk Technology in a High Availability Environment DRAFT Version 2.0, August 1996

DRAFT -- Revision 2.0
August 22, 1996Page 45
Purchase cost
Purchase cost is usually a factor in determining how much availability can be
provided. Cost is affected by:
the number of cabinets required
the number of I/O expansion modules (T500) required
the number of SCSI cards required
whether one- or two-level data redundancy is required
An example cost comparison among various standalone disks and disk arrays
follows the next section on footprint in Table K.
Footprint
The footprint is the amount of floor space required by the system. It changes
according to which disk technology is chosen. It is affected by:
the number of I/O expansion units required
whether UPSs are required
the number of cabinets required to hold the disks
Here is an example footprint and price comparison among five configurations
using LVM standalone disks, HADA disk arrays, and FLDAs and SCSI DAs for
64 GB of protected data. RAID 5 provides 64 GB of protected data using 80 GB
total disk space. LVM mirroring provides 64 GB of protected data using 128 GB
total disk space. This comparison includes the following assumptions:
space or cost for UPSs is not included
space or cost for T500 expansion modules is not included
standalone JBODs are configured in trays with four rather than
five mechanisms for simplicity of configuration and comparison with
the disk arrays whose capacities are multiples of 8 GB
the cache on the HADA, FLDA and SCSI DA divided among the
number of mechanisms in the array is equivalent to the cache on
each JBOD
1.6 meter cabinets are used that have room for up to 32 EIA
units and power capacity of 16 amperes at 230 VAC.
When reviewing the Table K, consider that Configuration A will probably
yield the greatest performance due to the larger number of mechanisms
spread over more F/W SCSI links. Configuration B, however, is the least
expensive and occupies the smallest floorspace.