Data set structure
數據集的結構
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.
使用數據集需要我們理解數據集的物理和邏輯結構和Z/OS如果訪問這些數據集的信息.
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.
數據集
在Z/OS中,數據集是一個已命名的內容相關數據記錄的集合,系統通過這個名字保存和訪問這些數據記錄.數據集相當于其他操作系統里面的文件.數據集是存儲在磁盤或者是磁帶里面的.
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)直接訪問存儲器
DASD 是磁盤設備的別名,它還有其他的同義詞disk volume, disk pack, or Head Disk Assembly (HDA).
Space
Disk space is allocated in units called cylinders, tracks, or blocks.
磁盤空間
磁盤空間以柱面,磁道,或者塊為單位作分配.
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
磁盤包含柱面,一個柱面是一個(CKD)設備上一個存儲單位,指向一個固定號碼的磁道.
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,它是磁盤表面的環形軌道,以磁性物質保存和被訪問數據信息. 磁道使用(CKD)格式,意味著每一個磁道包含一系列的字段,這些字段指明了磁道的開始位置和所用的空間,后面跟隨著數據記錄,數據記錄內保存三個字段,
.記數字段包含了記錄的長度
.關鍵字字段包含了可選的帳戶信息
.數據字段包含了用戶的實際數據
Count Key Data（CKD）是一種磁盤數據結構。每條物理磁盤記錄包含一個count區，一個可選的key，以及在一個記錄內間隔后面的數據data記錄。這個結構后面的原理就是：即然數據記錄的長度可能不同，它們就需要有一個統計字段來指示key和物理記錄的長度。統計區有以柱面頭記錄格式記錄的物理位置標識，Key的長度，和數據記錄的長度。Key要么沒有，要么是一串字符。大多數情況下是沒有key的，記錄順序排列，或者以直接柱面頭記錄定位。如果有key,則它通常是數據記錄前幾個字節的拷貝，但它可以是用來找到這條記錄的任何數據。這個key(還有記錄）都是通過硬件命令來定位的。Count Key Data Achitecture是由IBM在20世紀60年代創建的，用來作為System/360的磁盤驅動，也叫固定塊架構（Fixed Block Achitecture。
Record
記錄
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.
磁道包含記錄,一個記錄是一些包含了數據的字節.記錄是Z/OS上應用程序處理數據的基本單位.
• 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).
.記錄有一個邏輯記錄長度(LRECL)屬性,不同的DASD設備決定了數據記錄的最大長度的不同
.記錄可是定長的,也可以是變長的,傳統上,z/OS有5種記錄格式(RECFM),F固定,FB固定,分塊,V變長,VB變長,分塊,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.
塊
數據記錄群組成為數據塊,是寫入和讀取磁盤的單位.分塊的方式使數據處理更加高效,因為z/OS可以用一個塊的單位來讀寫記錄,而不是一個一個記錄單獨來讀寫.
塊大小(BLKSIZE),是指以F(固定)和FB(固定,分塊)格式的數據記錄寫入磁盤的塊的大小,對于分塊,V變長,VB變長,分塊,U格式的數據記錄,塊大小是數據集最大的可用數據物理塊大小.
Extents
擴展
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.
磁盤空間分配對于數據集來說包括(primary)第一次分配和二次(secondary)擴展,一個擴展分配了一定數量連續的磁盤磁道,柱面,或者塊.基于塊的讀寫方式下,使用磁盤擴展數據更加高效,應為讀寫連續的磁道是比讀寫零碎的數據快速很多.
Volume
卷
The term volume is often used to refer to a disk.
卷經常被認為是磁盤
Volume serial
卷名
The six-character name of a disk or tape volume, such as TEST01.
是磁盤或者磁帶的名字,6個字符,例如test01
Device type
設備類型
A model or type of disk device, such as 3390.
磁盤設備的型號或者是類型,例如3390
Organization
組織方式
The method of processing a data set, such as sequential.
處理數據的方式,例如順序訪問