在线、近线、离线存储都是什么

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在线存储

在线存储指存储设备和所存储的数据时刻保持“在线”状态,可供用户随意读取,满足计算平台对数据访问的速度要求。就像PC机中常用的磁盘存储模式一样。一般在线存储设备为磁盘和磁盘阵列等存储的设备,价格相对昂贵,但是性能较好。

近线存储

是随着客户存储环境的细化所提出的一个概念,所谓近线存储,外延相对广泛,主要定位于客户在线存储和离线存储间的应用。就是指那些并不是经常用到,或者说数据的访问量并不大的数据存放在性能较低的存储设备上。但同时对这些的设备要求是寻址迅速、传输率高。因此,近线存储对性能要求相对来说并不高,但要求相对较好的访问性能。同时多数情况下由于不常用的数据要占总数据量的比较大的比重,这也就要求近线存储设备在需要容量相对较大。简单一点的说就是把价值不同的数据分别放在不同性能的存储介质上进行存放。

离线存储

是指对在线存储数据的备份,以防范可能发生的数据灾难。离线存储的数据不常被调用,一般远离系统应用,所以人们就用“离线”来生动地描述这种存储方式。离线存储介质上的数据在读写时是顺序进行的。当需要读取数据时,需要把磁带卷到头,然后进行定位。当需要对已经写入的数据进行修改时,所有的数据都需要全部进行改写。因此,离线存储的访问速度慢、效率较低。离线存储典型产品是磁带库,价格相对低廉。

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