-## <a name="1 General"></a> 1 General
+[[!toc levels=3]]
-The General Section of the [[AFSFrequentlyAskedQuestions]].
-- [[PreambleFAQ]]
+## 1 General
-<div>
- <ul>
- <li><a href="#1 General"> 1 General</a><ul>
- <li><a href="#1.01 What is AFS?"> 1.01 What is AFS?</a></li>
- <li><a href="#1.02 Who supplies AFS?"> 1.02 Who supplies AFS?</a></li>
- <li><a href="#1.03 What is /afs?"> 1.03 What is /afs?</a></li>
- <li><a href="#1.04 What is an AFS cell?"> 1.04 What is an AFS cell?</a></li>
- <li><a href="#1.05 What are the benefits of u"> 1.05 What are the benefits of using AFS?</a><ul>
- <li><a href="#1.05.a Cache Manager"> 1.05.a Cache Manager</a></li>
- <li><a href="#1.05.b Location independence"> 1.05.b Location independence</a></li>
- <li><a href="#1.05.c Scalability"> 1.05.c Scalability</a></li>
- <li><a href="#1.05.d Improved security"> 1.05.d Improved security</a></li>
- <li><a href="#1.05.e Single systems image (SS"> 1.05.e Single systems image (SSI)</a></li>
- <li><a href="#1.05.f Replicated AFS volumes"> 1.05.f Replicated AFS volumes</a></li>
- <li><a href="#1.05.g Improved robustness to s"> 1.05.g Improved robustness to server crash</a></li>
- <li><a href="#1.05.h "Easy to use" networking"> 1.05.h "Easy to use" networking</a></li>
- <li><a href="#1.05.i Communications protocol"> 1.05.i Communications protocol</a></li>
- <li><a href="#1.05.j Improved system manageme"> 1.05.j Improved system management capability</a></li>
- </ul>
- </li>
- <li><a href="#1.06 Which systems is AFS avail"> 1.06 Which systems is AFS available for?</a></li>
- <li><a href="#1.07 What does "ls /afs" displa"> 1.07 What does "ls /afs" display in the Internet AFS filetree?</a></li>
- <li><a href="#1.08 Why does AFS use Kerberos"> 1.08 Why does AFS use Kerberos authentication?</a></li>
- <li><a href="#1.09 Does AFS work over protoco"> 1.09 Does AFS work over protocols other than UDP/IP?</a></li>
- <li><a href="#1.10 How can I access AFS from"> 1.10 How can I access AFS from my PC?</a></li>
- <li><a href="#1.11 How does AFS compare with"> 1.11 How does AFS compare with NFS?</a></li>
- </ul>
- </li>
- </ul>
-</div>
+The General Section of the [[AFSFrequentlyAskedQuestions]].
+- [[PreambleFAQ]]
- [[UsageFAQ]]
- [[AdminFAQ]]
- [[ResourcesFAQ]]
- [[AboutTheFAQ]]
- [[FurtherReading]]
-### <a name="1.01 What is AFS?"></a> 1.01 What is AFS?
+### 1.01 What is AFS?
AFS is a distributed filesystem that enables co-operating hosts (clients and servers) to efficiently share filesystem resources across both local area and wide area networks.
In November, 2000, IBM Open-Sourced AFS, creating [[OpenAFS]]. [[OpenAFS]] is under active development; as of this writing, the 1.6.4 release is being prepared for Unix-like platforms, and the 1.7 series for Windows is updated regularly.
-### <a name="1.02 Who supplies AFS?"></a> 1.02 Who supplies AFS?
+### 1.02 Who supplies AFS?
[[OpenAFS]] is available from the [[OpenAFS]] website. An independent open source project, Arla, supports some clients that [[OpenAFS]] does not, but has not been updated since release 0.90 in early 2007; the release of [[OpenAFS]] largely removed the reasons for the development of Arla and its sister project Milka (an open source AFS server).
</tr>
</table>
-### <a name="1.03 What is /afs?"></a> 1.03 What is `/afs`?
+### 1.03 What is `/afs`?
The root of the AFS filetree is `/afs`. If you execute `ls /afs`, you will see directories that correspond to AFS cells (see below). These cells may be local (on same LAN) or remote (e.g. halfway around the world).
With AFS you can access all the filesystem space under `/afs` with commands you already use (e.g. `cd`, `cp`, `rm`, and so on) provided you have been granted permission (see AFS ACL below).
-### <a name="1.04 What is an AFS cell?"></a> 1.04 What is an AFS cell?
+### 1.04 What is an AFS cell?
An AFS cell is a collection of servers grouped together administratively and presenting a single, cohesive filesystem. Typically, an AFS cell is a set of hosts that use the same Internet domain name.
Users log into AFS client workstations which request information and files from the cell's servers on behalf of the users.
-### <a name="1.05 What are the benefits of u"></a> 1.05 What are the benefits of using AFS?
+### 1.05 What are the benefits of using AFS?
The main strengths of AFS are its:
Here are some of the advantages of using AFS in more detail:
-#### <a name="1.05.a Cache Manager"></a> 1.05.a Cache Manager
+#### 1.05.a Cache Manager
AFS client machines run a Cache Manager process. The Cache Manager maintains information about the identities of the users logged into the machine, finds and requests data on their behalf, and keeps chunks of retrieved files on local disk.
Many modern NFS implementations provide metadata caching, but this caching is limited and the protocol support for it is somewhat weak, with the result that cached NFS can get out of sync with the server. NFS does not support file data caching at all, although some operating systems can be configured to make use of a separate cache filesystem module which must be configured separately from NFS on each client workstation and for each NFS mountpoint. As this cache is separate, it can only avoid becoming out of sync with the remote filesystem at the price of extra validation and additional network traffic to detect updates every time the file is accessed (or, if there is a delay set to minimize this traffic, it will "miss" remote changes made within that window); [[OpenAFS]]'s integrated cache, by comparison, will be notified of changes on the fileserver (by means of "callback breaking") and only needs to check explicitly for remote updates if the callback has expired (roughly 2 hours). In addition, for files on a read-only volume, it is sufficient to check for a volume update to revalidate all locally cached files on that volume.
-#### <a name="1.05.b Location independence"></a> 1.05.b Location independence
+#### 1.05.b Location independence
Unlike NFS, which makes use of a per-client mount table (such as `/etc/filesystems` on AIX or `/etc/fstab` on Linux) to map (mount) between a local directory name and a remote filesystem, AFS does its mapping (filename to location) at the server. This has the tremendous advantage of making the served filespace location independent.
(Actually, the AFS equivalent of `/home` would be `/afs/$AFSCELL/home`, where `$AFSCELL` is the AFS cellname.)
-#### <a name="1.05.c Scalability"></a> 1.05.c Scalability
+#### 1.05.c Scalability
With location independence comes scalability. An architectural goal of the AFS designers was client/server ratios of 200:1; some sites exceed this ratio. Exactly what ratio your cell can use depends on many factors including:
AFS cells can range from the small (1 server/client) to the massive (with hundreds of servers and thousands of clients). Cells can be dynamic: it is simple to add new fileservers or clients and grow the computing resources to meet new user requirements.
-#### <a name="1.05.d Improved security"></a> 1.05.d Improved security
+#### 1.05.d Improved security
Firstly, AFS makes use of Kerberos to authenticate users. This improves security for several reasons:
Some (not all) implmentations of NFS version 3 can use Kerberos authentication; NFS version 4 adds ACLs, but not all NFS4 implementations interoperate well. Additionally, configuring NFS to use Kerberos, even when it is supported, is often painful and can lead to interoperability problems.
-#### <a name="1.05.e Single systems image (SS"></a> 1.05.e Single systems image (SSI)
+#### 1.05.e Single systems image (SSI)
Establishing the same view of filestore from each client and server in a network of systems (that comprise an AFS cell) is an order of magnitude simpler with AFS than it is with, say, NFS.
1. on the same network as his cell and
2. his `ny.acme.com` cell is mounted in the `sf.acme.com` cell (as would certainly be the case in a company with two cells).
-#### <a name="1.05.f Replicated AFS volumes"></a> 1.05.f Replicated AFS volumes
+#### 1.05.f Replicated AFS volumes
AFS files are stored in structures called volumes. These volumes reside on the disks of the AFS file server machines. Volumes containing frequently accessed data can be read-only replicated on several servers.
An AFS client workstation will access the closest volume copy. By placing replicate volumes on servers closer to clients (eg on same physical LAN) access to those resources is improved and network traffic reduced.
-#### <a name="1.05.g Improved robustness to s"></a> 1.05.g Improved robustness to server crash
+#### 1.05.g Improved robustness to server crash
The Cache Manager maintains local copies of remotely accessed files. This is accomplished in the cache by breaking files into chunks of up to 64k (default chunk size). So, for a large file, there may be several chunks in the cache but a small file will occupy a single chunk (which will be only as big as is needed).
Also, if the AFS configuration has included replicated read-only volumes then alternate fileservers can satisfy requests for files from those volumes.
-#### <a name="1.05.h "Easy to use" networking"></a> 1.05.h "Easy to use" networking
+#### 1.05.h "Easy to use" networking
Accessing remote file resources via the network becomes much simpler when using AFS. Users have much less to worry about: want to move a file from a remote site? Just copy it to a different part of /afs.
Once you have wide-area AFS in place, you don't have to keep local copies of files. Let AFS fetch and cache those files when you need them.
-#### <a name="1.05.i Communications protocol"></a> 1.05.i Communications protocol
+#### 1.05.i Communications protocol
The AFS communications protocol is optimized for Wide Area Networks. Retransmitting only the single bad packet in a batch of packets and allowing the number of unacknowledged packets to be higher (than in other protocols, see [[[Johnson90|FurtherReading#Johnson90]]]).
-#### <a name="1.05.j Improved system manageme"></a> 1.05.j Improved system management capability
+#### 1.05.j Improved system management capability
Systems administrators are able to make configuration changes from any client in the AFS cell (it is not necessary to login to a fileserver).
Finally, the AFS clients were moved - this was noticed!
-### <a name="1.06 Which systems is AFS avail"></a> 1.06 Which systems is AFS available for?
+### 1.06 Which systems is AFS available for?
[[OpenAFS]], as of the 1.6.2 release for Unix and 1.7.24 for Windows, is currently available in binary releases for:
These are only the platforms for which official binary releases are prepared; it can be built from source for a large number of additional platforms including HP-UX, SGI, OpenBSD, NetBSD, and older releases and other CPU architectures of supported platforms.
-### <a name="1.07 What does "ls /afs" displa"></a> 1.07 What does `ls /afs` display in the Internet AFS filetree?
+### 1.07 What does `ls /afs` display in the Internet AFS filetree?
Essentially this displays the AFS cells that co-operate in the Internet AFS filetree.
Indeed, there are lots of benefits of using AFS on a local area network without using the WAN capabilities.
-### <a name="1.08 Why does AFS use Kerberos"></a><a name="1.08 Why does AFS use Kerberos "></a> 1.08 Why does AFS use Kerberos authentication?
+### 1.08 Why does AFS use Kerberos authentication?
It improves security.
For more detail on this and other Kerberos issues see the faq for Kerberos (posted to `news.answers` and `comp.protocols.kerberos`) [[[Jaspan|FurtherReading#Jaspan]]]. (Also, see [[[Miller87|FurtherReading#Miller87]]], [[[Bryant88|FurtherReading#Bryant88]]], [[[Bellovin90|FurtherReading#Bellovin90]]], [[[Steiner88|FurtherReading#Steiner88]]])
-### <a name="1.09 Does AFS work over protoco"></a> 1.09 Does AFS work over protocols other than UDP?
+### 1.09 Does AFS work over protocols other than UDP?
No. AFS was designed to work over UDP, and does not use TCP.
allow AFS to make use of other network transports, including TCP, but this is
still experimental and undergoing development.
-### <a name="1.10 How can I access AFS from"></a><a name="1.10 How can I access AFS from "></a> 1.10 How can I access AFS from my PC?
+### 1.10 How can I access AFS from my PC?
You can use [[OpenAFS]] for Windows client. In the past year it has become very stable and robust. [[OAfW]] works with Kerberos for Windows in much the same way the Unix clients work with Kerberos.
Mac OS X and Linux users might find [[`sshfs`|http://en.wikipedia.org/wiki/SSHFS]] useful in some circumstances.
-### <a name="1.11 How does AFS compare with"></a><a name="1.11 How does AFS compare with "></a> 1.11 How does AFS compare with NFS?
+### 1.11 How does AFS compare with NFS?
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