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A Network-attached storage or NAS device allows multiple machines to share the same storage over a network.
Prices, capacity, speed, and function all vary with price and size. The most important feature to be aware of are the protocols that a NAS appliance supports. The standard protocols are listed below.
Protocol Description NFS Network File System or NFS, popularly used with UNIX and Linux machines. SMB or CIFS Server Message Block used with Microsoft Windows operating systems. AFP AppleShare File Protocol used with Apple Mac OS X.
Software packages are available for each operating system to allow them to interoperate with servers using a different protocol, however there are limitations to that functionality and that determines what is required. There are two important versions of CIFS protocol to be aware of, the older version only supports certain character encodings such as English, Traditional Chinese, Japanese, etc, and importantly only one can be used at a time. The newer version of CIFS supports Unicode which allows multiple character sets to be used at the same time. Many of the consumer appliances do not support Unicode and might only offer a small selection of character encodings. A common problem would be that Traditional Chinese and Simplified Chinese file names cannot be used, although the contents of the files can be anything.
For storing of shared files a LTSP can use any NAS appliance that supports NFS or CIFS.
Using the みる directory server you can have diskless LTSP servers that store the operating system and the thin client software on the NAS appliances too, this functionality requires NFS. Certain features of NFS are also required:
➊ For security reasons most NFS servers by default map user id 0 to an anonymous account like nobody (65534).
Optional features that will help include.
➊ If the directory /common is exported with a subdirectory pictures/ you should also be able to mount /common/pictures. This allows the LTSP client to reside within the LTSP server tree, without submount support the directory will have to be mounted on top.
➋ This will be obvious, without locking the NFS mount might take upto a minute to complete you need to explicity set no locking to return to normal speeds.
➌ NFS over TCP is faster than UDP which has been the default.
If you cannot find a suitable NAS appliance the best option is to find an old computer or buy a new cheap desktop and install FreeNAS on it, for commercial varient use Open-E NAS. Cheap desktops in the US can be bought from RetroBox and Ebay, also consider local magazines for second hand sales. A HOWTO: Install FreeNAS is available for quick starting a LTSP environment with FreeNAS.
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It is recommended that any machine you use have a RAID 1 mirror setup to protect against disk failure, or a very good regular backup process. RAID 1 uses two disks each an exact copy so that if a hardware failure occurs in one the other can be used. Other RAID levels exist for managing configurations of three or more disk drives.
Computer components that have moving parts are highest on the list of items which are likely to fail. The power supply unit or PSU contains a fan for cooling, but the high power capacitors can also leak, start burning and fail. It is possible to purchase fault tolerant and hot swap PSUs for desktops but they are not common, they usually found in rack mounted servers.
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