Hard Disk Technologies (PATA (ATA), SATA, SCSI)
PATA: PATA, more commonly known in the past as ATA, represents Parallel Advanced Technology Attachment. Ranging in speeds from around 33Mbps to 133Mbps it is the cheapest form of hard disk around today.
SATA: The "s" stands for serial and represesents the evolution from PATA. Smaller serial cables and faster speeds starting at 150Mbps are the primary differentiators between PATA and SATA.
SCSI: SCSI stands for Small Computer Systems Interface. These disks have been around since the Ark. I am positive Noah himself used an array of these drives to maintain his animal inventory, not to mention their health records and diet requirements for the duration of the cruise.
Speeds range from 4Mbps through to the 160Mbps Ultra3 SCSI implementation. The successor touted to take over from SCSI is Fibre Channel. This serial data transfer technology increases the bandwidth available and uses optical fibre to connect the devices.
iSCSI: iSCSI is not directly related to disks, but while we were on the topic of SCSI we should discuss it. iSCSI stands for Internet Small Computer Systems Interface and is a relatively new standard used for sending SCSI storage commands over a IP network. The physical connection is usually a copper or fibre gigabit network connection. This is mostly used in SANs (more about those shortly).
Disk Array Technologies (NAS, DAS, SAN)
There are almost as many differing disk arrays as there are acronyms to match up with them. On top of that there is the ubiquitous RAID terminology to come to grips with.
NAS: NAS is an array (enclosure) of hard disks with a certain level of intelligence built into the box that allows administrators to access it and configure it to appear as a drive target on the network. The important factor with NAS is that it is like any other network attached appliance and is generally managed remotely via a Web interface or console connection.
DAS: DAS represents Direct Attached Storage, which is an array (enclosure) of hard disks with some limited intelligence which attaches directly to a server, these days usually with fibre connections but can also be SCSI too, which was the traditional method for DAS attachment.
SAN: SAN is Storage Area Network, which is not a specific disk-based technology like NAS and DAS. Indeed a SAN could comprise many differing technologies such as NAS, DAS, optical, and tape. SAN covers the whole concept of the enterprises interconnected information/data storage system(s). It is analogous to using the term Internet to describe the whole array of interconnected computer systems and servers around the world.
SAN targets can be configured to be available to users, workstations, servers etc, and can be located at various parts of the LAN or even over WAN links. The concept of a SAN is to remove the idea of storage being part of a server or workstation and incorporating it into the network. Theoretically SANs are easier to manage and expand as the need arises.
FCIP: On the topic of SANs, the term FCIP may sometimes be heard. FCIP represents Fibre Channel over Internet Protocol. Similar to iSCSI, Fibre Channel storage commands are sent over IP networks. According to Webopedia; "FCIP encapsulates Fibre Channel and transports it over a TCP socket. FCIP is considered a tunnelling protocol, as it makes a transparent point-to-point connection between geographically separated SANs over IP networks. FCIP relies on TCP/IP services to establish connectivity between remote SANs over LANs, MANs, or WANs. TCP/IP is also responsible for congestion control and management, as well as for data error and data loss recovery."
Other weird terminology associated with disks and drive arraysRAID: RAID has been around in some way, shape, or form for many years now. RAID represents Redundant Array of Inexpensive Disks -- it is also hotly debated that the "I" can also stand for independent -- so even the acronym pundits don't always agree either. As the name suggests, it provides some level of redundancy to a storage platform, although like most IT confusions, not necessarily so. There is RAID level 0 (which is striping data across two or more disks, generally for performance benefits).
There are at least 11 different types of RAID array levels that can be configured depending on one's choice of hardware and disk availability. These are most commonly represented as numbers, ie RAID 0 through to 7, then comes 10 (another IT confusion) and there is also RAID 0 + 1 (a striped mirror) and finally RAID S.
JBOD: Almost as good as RAID, this one means Just a Bunch of Disks. And for once the name pretty much says it all. A JBOD is a dumb chassis which is usually directly attached to a RAID controller and provides the housing and power for the disks.
Fabric: Not an acronym, but unfortunately equally as confusing as most of the others. The Fabric is the hardware that connects devices in a SAN together, so vendors like Cisco have Fabric switches which switch the fibre channel and/or iSCSI traffic from one device (say workstation or server) to the intended target (NAS, DAS, tape etc).
It is another term like SAN which tries to convey the impression that no single server or workstation is responsible for any one storage target -- sometimes referred to as any-to-any storage.
