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https://en.wikipedia.org/wiki/Clustered_file_system#Network-attached_storage says

Network-attached storage (NAS) provides both storage and a file system, like a shared disk file system on top of a storage area network (SAN). NAS typically uses file-based protocols (as opposed to block-based protocols a SAN would use) such as NFS (popular on UNIX systems), SMB/CIFS (Server Message Block/Common Internet File System) (used with MS Windows systems), AFP (used with Apple Macintosh computers), or NCP (used with OES and Novell NetWare).

https://en.wikipedia.org/wiki/Network-attached_storage

Network-attached storage (NAS) is a file-level (as opposed to block-level) computer data storage server connected to a computer network providing data access to a heterogeneous group of clients. NAS is specialized for serving files either by its hardware, software, or configuration. It is often manufactured as a computer appliance – a purpose-built specialized computer.[nb 1] NAS systems are networked appliances that contain one or more storage drives, often arranged into logical, redundant storage containers or RAID. Network-attached storage removes the responsibility of file serving from other servers on the network. They typically provide access to files using network file sharing protocols such as NFS, SMB, or AFP.

... A clustered NAS is a NAS that is using a distributed file system running simultaneously on multiple servers. The key difference between a clustered and traditional NAS is the ability to distribute[citation needed] (e.g. stripe) data and metadata across the cluster nodes or storage devices. Clustered NAS, like a traditional one, still provides unified access to the files from any of the cluster nodes, unrelated to the actual location of the data.

Does a NAS provide both block level and file level operations?

Does "Network-attached storage (NAS) provides both storage and a file system, like a shared disk file system on top of a storage area network (SAN)" mean that NAS and a shared disk file system on a SAN are the same?

Does "NAS typically uses file-based protocols (as opposed to block-based protocols a SAN would use) such as NFS (popular on UNIX systems), SMB/CIFS (Server Message Block/Common Internet File System) (used with MS Windows systems), AFP (used with Apple Macintosh computers), or NCP (used with OES and Novell NetWare)" mean that NAS and a distributed filesystem are the same?

Thanks.

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Nowadays the border between NAS and SAN is unclear especially for SMB products. Historically NAS devices consist of the bunch of disks arranged in some RAID to maximize the overall performance and achieve the required data redundancy. These devices have core operating systems aboard. Those OS do all low-level processing and file systems maintenance. File systems, in their turn, share disks content over the network on the file level. NAS present the storage over high-level protocols like SMB, NFS, AFP, etc. Modern NAS can also present block storage (iSCSI) and have basic SAN features like replication, snapshots, etc. If you need just “small” capacity (up to 100TB) and storage high availability is not required, modern NAS would be a best suitable option.

SAN is historically a block-level storage system that can be accessed via such fast protocols as FCoE, iSCSI, Fibre Channel, etc. Mostly SAN includes not only disk redundancy, but also controller redundancy and may allow active (or passive) replication between SAN boxes. SAN has flexible scalability option. And certainly, all enterprise level SAN know file protocols like CIFS and NFS.

Article regarding SAN and NAS - https://www.hyper-v.io/san-nas-public-cloud-lets-pick-secondary-storage/

Distributed filesystem is not a storage, but just a method how the storage access is organized and how the storage is presented. Actually, you can deploy distributed file system over (many) SAN/NAS devices. Here is an article with more explanations: https://www.quora.com/What-is-a-distributed-file-system-and-what-is-it-used-for

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It varies, but a NAS typically exposes file level storage rather then block level storage. Many NAS's are a variant of Linux or Another Unix variants running Windows file sharing (SMB) and Unix filesharing (NFS). It may be possible to do block level sharing, but I don't believe its a particularly common use case.

A SAN typically provides block level storage rather then file level storage.

A distributed filesystem is where the files are spread over many computers but behave as file storage.

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  • Thanks.I am still wondering what difference are between a NAS and a distributed filessytem? Could you elaborate more? – Tim Mar 29 at 10:06
  • A NAS is a single device while a distributed filesystem looks like a single file system but the files are ispread across multiple devices – davidgo Mar 29 at 18:44
  • Thanks. NAS is Network-attached storage (NAS). In what sense do you mean by NAS is a "single device"? Isn't it the same as a distributed file system? – Tim Mar 29 at 19:37
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    A NAS is a single computer (ie box with CPU, ram+disk). A distributed filesystem is entirely different - the files are scattered over more then 1 computer/device even though they look, to the end user to all be at a single location... – davidgo Mar 29 at 19:42
  • Distributed filesystems are not common as they are hard to build and maintain. They have very specific use cases (generally storing more data then can be stored on a single device) and are seldom seen outside of "big data" companies, the military or institutions requiring massive storage. – davidgo Mar 29 at 19:46
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SAN: filesystem - > network - > block device

NAS: network - > filesystem - > block device

IOW, SAN makes block devices accessible over the network. The storage server stores only blocks without any knowledge how they build a filesystem, if at all. In opposite, NAS makes filesystem accessible over the network. The NAS server exports it's local file system.

Often, NAS servers use SAN to store the data. For example, an NFS server can export local XFS file system wich is attached by iSCSI.

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  • waht is shared disk file system? – BAKE ZQ Jul 11 at 7:08
  • @BAKEZQ shared disk filesystem is a type of SAN, where multiple hosts can access the same block device. A NFS 4.1/pNFS with block layout driver over iSCSI it an example of it. The access to blocks coordinated by nfs server, however the clients directly talk to block devices. – kofemann Jul 20 at 21:34

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