Archive & Backup 概念

Archive & Backup

提起归档和备份两个词，给人感觉上是相同的概念，就是对指定文件的一个copy而已。archive和backup感觉是相似的，但是他们有着明显的不同de。

archive

An archive is a collection of data moved to repository for backup,to keep separate for compliance reasons or for moving off primary storage media.
档案是一个被移到仓库备份的数据的集合。变为档案这一动作，我们叫归档，归档需要将进行归档数据移出主存媒介，或者其它方式将归档数据与现网在用数据¹合理地隔离开来
It can include a simple list of files or files organized under a directory or catalog structure(depending on how a particular program supports archiving)
_档案可以包括一个简单的文件列表，或者通过目录或者catalog structure组织文件（依据特特定程序支持怎样归档）
Web and File Transfer Protocol sites that provide downloadable software programs sometimes refer to the list of downloadable files as an archive or archives.
_有些提供下载程序的网页和文件站点，通常将可供下载的程序列表作为归档。

Backup vs. archive

While data backup and archiving are similar, the have distinct difference.
Backups are copies of data stored for the purpose of recovery in the case of corruption.
These copies are typically created using replication or mirroring and are updated as files change.
It is short-term storage that needs to perform well enough to restore data quickly.
Backups are usually stored as blocks to facilitate the recovery of large amounts of data at one time.

Archived data is not a copy,but rather inactive an rarely altered data that needs to be retained for long periods of time.
相比备份的源数据，归档的源数据相对来说是不平凡极少再改动的数据，已经形成了一个稳定的版本的数据。这种数据需要长期保持。
Performance is less critical in archive storage.
档案对存储媒介性能不是要求那么重要。比如i/o，检索查询速度等。
Rather than stored in blocks,archived data is usually stored as a file or object that can be stored with metadata attached so that granular access to data is possible.
相比通过块存储，归档数据通常打包为一个文件或者能够附加上metadata数据的存储对象中，这样可以通过已颗粒方式从归档中访问数据。

Archive storage options

Archive storage typically needs to be able to store large amounts of data,for long periods of time at a low cost.
The following storage options are commonly used for archived data:

• Tape 磁带 花费很小，但是访问效率实在太低了相比其它文档存储选择。由于这个特点，所以适合很长时间的档案存储，几乎不需要被访问。
• Disk 磁盘(Hard disk drives) 电力和冷却是硬盘存储的一个花销。
• Cloud 云 云存档是最受欢迎归档方式，因为它可以容易的扩展和移除在硬件、电力、冷却上的花销。然而，对于大的数据中心持续增长的归档数据，云存储的开销也会随着增长。一些主要的云存储提供商提供的云存储平台都是低性能低花销的。
• Object 对象 是一个有效的归档存储方式，因为它有能力存储大量的metadata²,metadata是轻松访问数据至关重要的部分。Object storage 也是低花销，可以存储大量数据的。

很多情况下many cases,归档和备份软件是被整合在一起的。some software also offers the ability to cache segments of archived data on disk ,while the majority is stored on object or tape to improve response times when data is accessed.
有些软件也提供缓存归档数据部分在磁盘上，主要部分还是存储在对象或者磁带中，为的是提高快速响应数据访问请求。

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1. 相对于归档数据，就是最新版本在用的数据。↩

2. 用于描述其它data的data。metadata是data的基础信息总结。例如：author，date created,date modified,file size 等，通过metadata能够快速地过滤定位需要定位的document。metadata除了用于文档，还用于images,videos,spreadsheets and web pages.web pages对metadata的使用非常常见。metadata添加可以可以手动也可以程序自动。↩