Cisco Headend System Release 2.7 Installation Guide
Appendix D
Storage Requirements
Storage Requirements
40
SR i4.5 Storage Requirements
The computing industry has many acronyms for storage interfaces (IDE, ATA,
PATA, SATA, SCSI, FC, and others). Some are even acronyms of acronyms (SAS:
Serial Attached SCSI). These acronyms represent specific physical interfaces to
storage and ‘command sets’ that are used to read and write to or from that storage.
This appendix will not try to explain these interfaces, but instead discuss broader
categories of how a computer accesses these interfaces.
How computers access storage generally falls into one of three categories: Direct
Attached Storage (DAS), Storage Attached Network (SAN), and Network Attached
Storage (NAS). Each of these terms is explained in the following sections.
PATA, SATA, SCSI, FC, and others). Some are even acronyms of acronyms (SAS:
Serial Attached SCSI). These acronyms represent specific physical interfaces to
storage and ‘command sets’ that are used to read and write to or from that storage.
This appendix will not try to explain these interfaces, but instead discuss broader
categories of how a computer accesses these interfaces.
How computers access storage generally falls into one of three categories: Direct
Attached Storage (DAS), Storage Attached Network (SAN), and Network Attached
Storage (NAS). Each of these terms is explained in the following sections.
Direct Attached Storage (DAS) or Direct Attached Storage Device (DASD)
Direct attached storage refers to a storage device that is directly connected to the
computer with whatever interface is on the device. In this situation, the storage
device is under the control of the computer. Examples of DAS range from a single
ATA disk drive connected to a PC, to a SCSI tape drive inside or nearby a server, to a
separate enclosure of disks connected to the computer via a SCSI or Fibre Channel
(FC) cable. If the computer is connected to a network, the storage could be offered to
other computers on the network and would appear to those other computers as
NAS.
computer with whatever interface is on the device. In this situation, the storage
device is under the control of the computer. Examples of DAS range from a single
ATA disk drive connected to a PC, to a SCSI tape drive inside or nearby a server, to a
separate enclosure of disks connected to the computer via a SCSI or Fibre Channel
(FC) cable. If the computer is connected to a network, the storage could be offered to
other computers on the network and would appear to those other computers as
NAS.
Storage Area Network (SAN)
Storage area network (SAN) is a dedicated network built for sharing storage devices
among multiple computers. Typically a SAN is built with Fibre Channel interfaces
on computers, and storage devices with one or more Fibre Channel switches. SAN
networks are generally built to provide ‘block level’ access to storage. Disk space on
a storage device is configured into pieces that are presented to the network as a
Logical Unit Number (LUN). A SAN switch is configured to control what computer
is able to access which LUN. Computers or hosts access these LUNs using a Fibre
Channel host bus adapter (HBA). While a disk array is connected to the SAN via a
Fibre Channel interface, what interface the disks use inside the array can vary.
Traditionally, disks in a Fibre Channel array have Fibre Channel interfaces
themselves, but many arrays today that have external Fibre Channel interfaces use
SAS or SATA interface disks internally.
among multiple computers. Typically a SAN is built with Fibre Channel interfaces
on computers, and storage devices with one or more Fibre Channel switches. SAN
networks are generally built to provide ‘block level’ access to storage. Disk space on
a storage device is configured into pieces that are presented to the network as a
Logical Unit Number (LUN). A SAN switch is configured to control what computer
is able to access which LUN. Computers or hosts access these LUNs using a Fibre
Channel host bus adapter (HBA). While a disk array is connected to the SAN via a
Fibre Channel interface, what interface the disks use inside the array can vary.
Traditionally, disks in a Fibre Channel array have Fibre Channel interfaces
themselves, but many arrays today that have external Fibre Channel interfaces use
SAS or SATA interface disks internally.