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Data set structure
数据集的结构
 
Working with data sets requires an understanding of the physical and logical structure of a data set, and how z/OS® accesses information in the data set.
使用数据集需要我们理解数据集的物理和逻辑结构和Z/OS如果访问这些数据集的信息.
Data set
In z/OS, a data set is a named collection of related data records that is stored and retrieved by an assigned name. A data set is equivalent to a file in other operating systems. Data sets are stored on tape or disks.
数据集
    在Z/OS中,数据集是一个已命名的内容相关数据记录的集合,系统通过这个名字保存和访问这些数据记录.数据集相当于其他操作系统里面的文件.数据集是存储在磁盘或者是磁带里面的.
Direct Access Storage Device (DASD)
DASD is another name for a disk drive. Additional synonyms include: disk volume, disk pack, or Head Disk Assembly (HDA).
(DASD)直接访问存储器
DASD 是磁盘设备的别名,它还有其他的同义词disk volume, disk pack, or Head Disk Assembly (HDA).
Space
Disk space is allocated in units called cylinders, tracks, or blocks.
磁盘空间
    磁盘空间以柱面,磁道,或者块为单位作分配.
Cylinder
A disk drive contains cylinders. A cylinder is a unit of storage on a count-key-data (CKD) device with a fixed number of tracks.
柱面
    磁盘包含柱面,一个柱面是一个(CKD)设备上一个存储单位,指向一个固定号码的磁道.
Track
Cylinders contain tracks, which are circular paths on the surface of a disk or diskette on which information is magnetically recorded and from which recorded information is read. Tracks are in count-key-data (CKD) format, which means that each track contains fields that indicate the start of the track and the space used, followed by records containing three fields:
The count field defines the length of the record
The key field contains optional accounting information
The data field contains the user data
磁道
柱面包含磁道,它是磁盘表面的环形轨道,以磁性物质保存和被访问数据信息. 磁道使用(CKD)格式,意味着每一个磁道包含一系列的字段,这些字段指明了磁道的开始位置和所用的空间,后面跟随着数据记录,数据记录内保存三个字段,
.记数字段包含了记录的长度
.关键字字段包含了可选的帐户信息
.数据字段包含了用户的实际数据
Count Key Data(CKD)是一种磁盘数据结构。每条物理磁盘记录包含一个count区,一个可选的key,以及在一个记录内间隔后面的数据data记录。这个结构后面的原理就是:即然数据记录的长度可能不同,它们就需要有一个统计字段来指示key和物理记录的长度。统计区有以柱面头记录格式记录的物理位置标识,Key的长度,和数据记录的长度。Key要么没有,要么是一串字符。大多数情况下是没有key的,记录顺序排列,或者以直接柱面头记录定位。如果有key,则它通常是数据记录前几个字节的拷贝,但它可以是用来找到这条记录的任何数据。这个key(还有记录)都是通过硬件命令来定位的。Count Key Data Achitecture是由IBM在20世纪60年代创建的,用来作为System/360的磁盘驱动,也叫固定块架构(Fixed Block Achitecture。
Record
记录
Tracks contain records. A record is some number of bytes containing data. The record is the basic unit of information used by a program running on z/OS.
磁道包含记录,一个记录是一些包含了数据的字节.记录是Z/OS上应用程序处理数据的基本单位.
Records have a logical record length (abbreviated as LRECL); different types of DASD impose different maximum lengths for records.
Records are either fixed length or variable length in a given data set. Traditional z/OS data sets have one of five record formats (abbreviated as RECFM): Fixed (F), fixed blocked (FB), variable (V), variable blocked (VB), or undefined (U).
.记录有一个逻辑记录长度(LRECL)属性,不同的DASD设备决定了数据记录的最大长度的不同
.记录可是定长的,也可以是变长的,传统上,z/OS有5种记录格式(RECFM),F固定,FB固定,分块,V变长,VB变长,分块,U未知
Blocks
Records can be grouped into data blocks, which are the units of recording on disk. Blocking makes processing more efficient because z/OS can access an entire block at once instead of reading or writing records individually.
Block size (abbreviated as BLKSIZE) is the physical block size written on the disk for fixed (F) and fixed block (FB) records. For variable and undefined (V, VB, and U) records, block size is the maximum physical block size that can be used for the data set.
数据记录群组成为数据块,是写入和读取磁盘的单位.分块的方式使数据处理更加高效,因为z/OS可以用一个块的单位来读写记录,而不是一个一个记录单独来读写.
块大小(BLKSIZE),是指以F(固定)和FB(固定,分块)格式的数据记录写入磁盘的块的大小,对于分块,V变长,VB变长,分块,U格式的数据记录,块大小是数据集最大的可用数据物理块大小.
Extents
扩展
Space for a disk data set is assigned in primary and secondary extents. An extent is a contiguous number of disk drive tracks, cylinders, or blocks. Data sets can increase in extents as they grow. As with blocking, the use of extents is more efficient because reading or writing contiguous tracks is faster than reading or writing data that is scattered over the disk.
磁盘空间分配对于数据集来说包括(primary)第一次分配和二次(secondary)扩展,一个扩展分配了一定数量连续的磁盘磁道,柱面,或者块.基于块的读写方式下,使用磁盘扩展数据更加高效,应为读写连续的磁道是比读写零碎的数据快速很多.
Volume
The term volume is often used to refer to a disk.
卷经常被认为是磁盘
Volume serial
卷名
The six-character name of a disk or tape volume, such as TEST01.
是磁盘或者磁带的名字,6个字符,例如test01
Device type
设备类型
A model or type of disk device, such as 3390.
磁盘设备的型号或者是类型,例如3390
Organization
组织方式
The method of processing a data set, such as sequential.
处理数据的方式,例如顺序访问
posted on 2013-07-29 11:36 Eric_jiang 阅读(356) 评论(0)  编辑  收藏 所属分类: Mainframe

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