06-29-2004
I've always believed that there is a bit of confusion in terms that people use. I have always thought of NAS as Network Area STORAGE and SAN as Storage Area NETWORK. Anything that connects to this special network is a NAS device and it runs on a SAN. That SAN can be ethernet or fibre channel. However, I think that the common usage for most people is that SAN means fibre channel network and NAS means ethernet.
So by that definition a SAN is a network of fibre channel (a protocol) connected by either copper wires or fiber optic cables. Each device on this SAN connects through an HBA (hardware bus adapter) and 1 or more fibre channel switches. When the SAN is first installed every device on that SAN can see every other device such as a server, a tape drive, a disk drive, a tape library, disk array, etc. The SAN administrator will then set up paths to allow certain devices to "see" only certain devices and block paths to other devices. It is possible to have more than 1 computer using a certain device. This is sometimes used for clustering failover or pehaps a shared tape drive.
When you boot your computer it will see every device on the SAN that it has access to and it will look like a locally attached disk to your computer. There is no security for these devices other than that path. For example, if both a unix server and an NT server see the same drive the NT system will not know about the unix system and will claim it as its own and write its own header on that drive destroying the data for the unix system. Many people will refer to their disk array as their SAN but in reality the SAN is the network connecting the disk array. You may call the array a SAN device but not a SAN itself.
I may be slightly off on some of this and please correct me if I am wrong but this is always how I've thought of it.
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json(3tcl) JSON json(3tcl)
__________________________________________________________________________________________________________________________________________________
NAME
json - JSON parser
SYNOPSIS
package require Tcl 8.4
package require json ?1.1.2?
::json::json2dict txt
_________________________________________________________________
DESCRIPTION
The json package provides a simple Tcl-only library for parsing the JSON http://www.json.org/ data exchange format as specified in RFC 4627
http://www.ietf.org/rfc/rfc4627.txt. There is some ambiguity in parsing JSON because JSON has type information that is not maintained by
the Tcl conversion. The json package returns data as a Tcl dict. Either the dict package or Tcl 8.5 is required for use.
COMMANDS
::json::json2dict txt
Parse JSON formatted text txt into a Tcl dict and return the value.
EXAMPLES
An example of a JSON array converted to Tcl. A JSON array is returned as a single item with multiple elements.
[
{
"precision": "zip",
"Latitude": 37.7668,
"Longitude": -122.3959,
"Address": "",
"City": "SAN FRANCISCO",
"State": "CA",
"Zip": "94107",
"Country": "US"
},
{
"precision": "zip",
"Latitude": 37.371991,
"Longitude": -122.026020,
"Address": "",
"City": "SUNNYVALE",
"State": "CA",
"Zip": "94085",
"Country": "US"
}
]
=>
{Country US Latitude 37.7668 precision zip State CA City {SAN FRANCISCO} Address {} Zip 94107 Longitude -122.3959} {Country US Latitude 37.371991 precision zip State CA City SUNNYVALE Address {} Zip 94085 Longitude -122.026020}
An example of a JSON object converted to Tcl. A JSON object is returned as a multi-element list (a dict).
{
"Image": {
"Width": 800,
"Height": 600,
"Title": "View from 15th Floor",
"Thumbnail": {
"Url": "http://www.example.com/image/481989943",
"Height": 125,
"Width": "100"
},
"IDs": [116, 943, 234, 38793]
}
}
=>
Image {IDs {116 943 234 38793} Thumbnail {Width 100 Height 125 Url http://www.example.com/image/481989943} Width 800 Height 600 Title {View from 15th Floor}}
BUGS, IDEAS, FEEDBACK
This document, and the package it describes, will undoubtedly contain bugs and other problems. Please report such in the category json of
the Tcllib SF Trackers [http://sourceforge.net/tracker/?group_id=12883]. Please also report any ideas for enhancements you may have for
either package and/or documentation.
KEYWORDS
data exchange, exchange format, javascript, json
CATEGORY
CGI programming
COPYRIGHT
Copyright (c) 2006 ActiveState Software Inc.
Copyright (c) 2009 Thomas Maeder, Glue Software Engineering AG
json 1.1.2 json(3tcl)