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NAS(Network Attached Storage，网络附属存储)是一种 将分布、独立的数据整合为大型、集中化管理的数据中心 ，以便于对不同主机和应用服务器进行访问的技术。按字 面简单说就是连接在网络上, 具备资料存储功能的装置， 因此也称为“网络存储器”。 NAS被定义为一种特殊的专用数据存储服务器，包括存储 器件(例如磁盘阵列、CD/DVD 驱动器、磁带驱动器或可移 动的存储介质)和内嵌系统软件，可提供跨平台文件共享 功能。NAS通常在一个LAN上占有自己的节点，无需应用服 务器的干预，允许用户在网络上存取数据，在这种配置中 ，NAS集中管理和处理网络上的所有数据，将负载从应用 或企业服务器上卸载下来，有效降低总拥有成本，保护用 户投资。 NAS本身能够支持多种协议(如NFS、CIFS、FTP、HTTP等) ，而且能够支持各种操作系统。通过任何一台工作站，采 用IE或Netscape浏览器就可以对NAS设备进行直观方便的 管理。 NAS的外观： NAS是功能单一的精简型电脑，因此在架构上不像个人电 脑那么复杂，像键盘、鼠标、荧幕、音效卡、喇叭、扩充 漕、各式连接口等都不需要；在外观上就像家电产品，只 需电源与简单的控制钮。NAS在架构上与个人电脑相似， 但因功能单纯，可移除许多不必要的连接器、控制晶片、 电子回路，如键盘、鼠标、USB、VGA等。 NAS简介 简称，中文称为网络附加存储。在NAS存储结构中，存储 系统不再通过I/O总线附属于某个服务器或客户机，而直 接通过网络接口与网络直接相连，由用户通过网络访问。 NAS实际上是一个带有瘦服务器的存储设备，其作用类似 于一个专用的文件服务器。这种专用存储服务器去掉了通 用服务器原有的不适用的大多数计算功能，而仅仅提供文 件系统功能。与传统以服务器为中心的存储系统相比，数 据不再通过服务器内存转发，直接在客户机和存储设备间 传送，服务器仅起控制管理的作用。 NAS的主要特点 NAS 使用了传统以太网协议，当进行文件共享时，则利用了 NFS和CIFS以沟通NT和Unix系统。由于NFS和CIFS都是基于 操作系统的文件共享协议，所以NAS的性能特点是进行小 文件级的共享存取。 NAS设备是直接连接到以太网的存储 器，并以标准网络文件系统如NFS、SMB/CIFS over TCP/IP接口向客户端提供文件服务。NAS设备向客户端提 供文件级的服务。但内部依然是以数据块的层面与它的存 储设备通讯。文件系统是在这个NAS 存储器里。 NAS的主 要长处第一，NAS适用于那些需要通过网络将文件数据传 送到多台客户机上的用户。NAS设备在数据必须长距离传 送的环境中可以很好地发挥作用。第二，NAS设备非常易 于部署。可以使NAS主机、客户机和其他设备广泛分布在 整个企业的网络环境中。NAS可以提供可靠的文件级数据 整合，因为文件锁定是由设备自身来处理的。 第三，NAS 应用于高效的文件共享任务中，例如UNIX中的NFS和 Windows NT中的CIFS，其中基于网络的文件级锁定提供了 高级并发访问保护的功能。 最后，在某些情况下，企业 可以有限地为数据库应用部署NAS解决方案。 NAS分类 1 、电器型服务器 电器型服务器是NAS系列设备中最低端的 产品。电器型服务器不是专门附加的存储设备。它们为网 络提供了一个存储的位置，但是由于没有冗余的以及和高 性能的组件，它们相对比较便宜。在工作组环境中，电器 型服务器要起很多作用。典型服务包括网络地址翻译 （NAT）、代理、DHCP、电子邮件、Web服务器、DNS、防 火墙和VPN。 2、工作组NAS 工作组级的NAS特别适合于存 储需求相对较低的小型和中型公司，它们的存储需要一般 从几百GB到1TB。运行电子商务软件或者大型数据库的公 司会需要几 TB的存储空间，他们使用的属于中型NAS。 一般来说，当从工作组升级到中型NAS时，你会发现热插 拔驱动器和一些可以放置额外的驱动器或更多的故障恢复 产品的设备盒、增强的管理功能以及系统复杂性的少许提 高。 3、中型NAS 我们所说的中型NAS解决方案提供了更 好的扩展性和可靠性，而且有着与低端NAS类似的优点， 例如方便、专用的存储空间和简单的安装和管理过程。与 电器型服务器和工作组级NAS相比，这些NAS设备的成本明 显要高很多。 4、大型NAS 这类存储设备，系统的易扩展 性以及高可用性和冗余性都是十分关键的。这些设备还必 须提供高端服务器的性能、灵活的管理以及与异类网络平 台交互的能力。 意思是“网络附加存储”。按字面简单说就是连接在网络 上, 具备资料存储功能的装置，因此也称为“网络存储器 ”或者“网络磁盘阵列”。 上不像个人电脑那么复杂，在外观上就像家电产品，只需 电源与简单的控制钮，NAS是一种专业的网络文件存储及 文件备份设备，它是基于LAN（局域网）的，按照TCP/IP 协议进行通信，以文件的I/O（输入/输出）方式进行数据 传输。在LAN环境下， NAS已经完全可以实现异构平台之 间的数据级共享，比如NT、UNIX等平台的共享。一个NAS 系统包括处理器，文件服务管理模块和多个硬盘驱动器( 用于数据的存储)。 NAS 可以应用在任何的网络环境当中 。主服务器和客户端可以非常方便地在NAS上存取任意格 式的文件，包括SMB格式（Windows）NFS格式(Unix, Linux)和CIFS（Common Internet File System）格式等 等。典型的NAS的网络结构 或需共享的数据提供存储空间。利用NAS本身具有的 SnapShot(快照)功能，在NAS上可制定自动的快速备份策 略，将其上的重要数据进行备份恢复。 驱动器的方式实现文件共享 (将数据信息直接保存在NAS存储上) 员或用户本人通过“快照”选择不同时间的文件版本进行 快速的文件恢复 Professional为IP网络上的笔记本及PC机提供备份数据存 储空间 Professional Console Management软件 Backup Server软件，在安装时要选择足够大的目录为客 户机提供足够的存储空间 professional Client软件 需要备份的客户机制定备份策略组 的备份策略实施了 实施及管理简便 NBP的安装及管理也极为方便 速保存和恢复及完整的在线备份 上制作灾难恢复启动光盘来进行灾难恢复 新传送整个文件 备份服务器，从而有效的减少网络负载 包括 Outlook 的 PST 文件 重新进行，以保证备份的数据完整 Description NAS hardware is similar to the traditional file server equipped with direct attached storage. However it differs considerably on the software side. The operating system and other software on the NAS unit provides only the functionality of data storage, data access and the management of these functionalities. Use of NAS devices for other purposes (like scientific computations or running database engine) is strongly discouraged. Many vendors also purposely make it hard to develop or install any third-party software on their NAS device by using closed source operating systems and protocol implementations. In other words, NAS devices are server appliances. NAS units also usually have a web interface as opposed to monitor/keyboard/mouse. Often minimal-functionality or stripped-down operating systems are used on NAS devices. For example FreeNAS, which is open source NAS software meant to be deployed on standard computer hardware, is in fact a "leaned-out" version of FreeBSD. NAS systems usually contain one or more hard disks, often arranged into logical, redundant storage containers or RAIDs (redundant arrays of independent disks), as do traditional file servers. NAS removes the responsibility of file serving from other servers on the network. NAS uses file-based protocols such as NFS (popular on UNIX systems) or SMB (Server Message Block) (used with MS Windows systems). NAS unit rarely limits clients to only one protocol. NAS provides both storage and filesystem. This is often contrasted with SAN (Storage Area Network), which provides only block-based storage and leaves filesystem concerns on the "client" side. SAN protocols are SCSI, Fibre Channel, iSCSI, ATA over Ethernet, or HyperSCSI. The boundaries between NAS and SAN systems are also starting to overlap, with some products making the obvious next evolution and offering both file level protocols (NAS) and block level protocols (SAN) from the same system. However a SAN device is usually served through NAS as one large flat file, not as a filesystem per se. An excellent example of this is Openfiler the opensource product running on Linux. Image:SANvsNAS.svg [edit] History Network-attached storage was introduced with the early file sharing Novell's NetWare server operating system and NCP protocol in 1983. In the UNIX world, Sun Microsystems' 1984 release of NFS allowed network servers to share their storage space with networked clients. 3Com's 3Server and 3+Share software was the first purpose-built servers (including proprietary hardware, software, and multiple disks) for open systems servers, and the company led the segment from 1985 through the early 1990s. 3Com and Microsoft would develop the LAN Manager software and protocol to further this new market. Inspired by the success of file servers from Novell, IBM, and Sun, several firms developed dedicated file servers. While 3server was among the first firms to build a dedicated NAS for desktop operating systems, Auspex Systems was one of the first to develop a dedicated NFS server for use in the UNIX market. A group of Auspex engineers split away to create the integrated Network Appliance "filer", which supported both Windows and UNIX, in the early 1990s, starting the market for proprietary NAS arrays. Starting in the early 2000s, a series of startups emerged offering alternative solutions to single filer solutions in the form of clustered NAS - Exanet, IBRIX, Isilon, PolyServe to name a few. [edit] Benefits Availability of data might potentially be increased with NAS if it provides built-in RAID and clustering. Performance can be increased by NAS because the file serving is done by the NAS and not done by a server responsible for also doing other processing. The performance of NAS devices, though, depends heavily on the speed of and traffic on the network and on the amount of cache memory (RAM) on the NAS computers or devices. It should be noted that NAS is effectively a server in itself, with all major components of a typical PC – a CPU, motherboard, RAM, etc. – and its reliability is a function of how well it is designed internally. A NAS without redundant data access paths, redundant controllers, redundant power supplies, is probably less reliable than DAS connected to a server which does have redundancy for its major components. [edit] Drawbacks Due to the multiprotocol, and the reduced CPU and OS layer, the NAS has its limitations compared to the DAS/FC systems. If the NAS is occupied with too many users, too many I/O operations, or CPU processing power that is too demanding, the NAS reaches its limitations. A server system is easily upgraded by adding one or more servers into a cluster, so CPU power can be upgraded, while the NAS is limited to its own hardware, which is in most cases not upgradeable. NAS will also fail to expose well-known services that are typical of a file server, or enable them in a way that is not efficient. Examples are: ability to compute disk usage of separate directories, ability to index files rapidly (locate), ability to mirrorize efficiently with rsync. You may still rsync, but through a NFS client; that method fails to enumerate huge file hierarchies at the nominal speed of local drives and induces important network traffic. The key difference between DAS and NAS is that DAS is simply an extension to an existing server and is not networked while NAS sits on a network as its own entity; it is easier to share files with NAS. NAS typically has less CPU and I/O power compared to DAS. [edit] Security concerns Security may be increased because of NAS simplicity and lack of superfluous software, however closed-source development model of NAS leads to security through obscurity, which has proven to be inaccurate. [edit] Security when connected to Internet NAS drives are generally safe to place on a network if connected to the internet, however there are some security concerns that need to be addressed by administrators. Some NAS drives (like the LANdrive for example) are based on a Linux operating system and are open source. There are a numerous firmware upgrades on the internet produced by various sources and NAS drive users are often tempted to upgrade their firmware to overcome problems and issues they have experienced. Inadvertently extra features may be added which can compromise the security of the NAS drive and network. Some NAS drives also have FTP servers built in. [edit] NAS uses NAS is useful for more than just general centralized storage provided to client computers in environments with large amounts of data. NAS can enable simpler and lower cost systems such as load-balancing and fault-tolerant email and web server systems by providing storage services. The potential emerging market for NAS is the consumer market where there is a large amount of multi- media data. Such consumer market appliances are now commonly available. Unlike their rackmounted counterparts, they are generally packaged in smaller form factors. The price of NAS appliances has plummeted in recent years, offering flexible network based storage to the home consumer market for little more than the cost of a regular USB or FireWire external hard disk. Many of these home consumer devices are built around ARM, PowerPC or MIPS processors running an embedded Linux operating system. Examples include Buffalo's TeraStation [1] and Linksys NSLU2 [2]. More recently, home NAS devices have incorporated support for the Universal Plug and Play protocol, enabling them to serve the growing number of networked home media players. [edit] NAS heads A NAS head refers to a NAS which does not have any on-board storage, but instead connects to a SAN. In effect, it acts as a translator between the file-level NAS protocols (NFS,CIFS,etc.) and the block-level SAN protocols (Fibre Channel, iSCSI). Thus it can combine the advantages of both technologies. The term "NAS head" is sometimes also used to refer to the portion of a self- contained NAS system other than its storage. An example would be the ONStor Bobcat. [edit] NAS operating systems for consumer PCs Open source NAS-oriented distributions of Linux and FreeBSD are also available, including FreeNAS, NASLite and Openfiler. They are easy to configure via a Web-based Interface and run on low-end conventional computers. They can run from a LiveCD, bootable USB flash drive, or from one of the mounted hard drives. They run Samba, NFS daemon, and FTP daemons which are freely available for those operating systems. |
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