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[Imported from Trac: page FAQ, version 103]
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FAQ.md

@ -4,7 +4,7 @@ A: Think of Tahoe-LAFS as being like [BitTorrent](https://en.wikipedia.org/wiki/
**<a name="Q1_why_tahoe_lafs">Q1:</a> What is special about Tahoe-LAFS? Why should anyone care about it instead of [other distributed storage systems](RelatedProjects#OtherProjects)?**
A1: Tahoe-LAFS is the first Free !Software/Open Source storage technology to offer *provider-independent security*. *Provider-independent security* means that the integrity and confidentiality of your files is guaranteed by mathematics computed on the client side, and is independent of the servers, which may be owned and operated by someone else. To learn more, read [our one-page explanation]source:git/docs/about.rst.
A1: Tahoe-LAFS is the first Free !Software/Open Source storage technology to offer *provider-independent security*. *Provider-independent security* means that the integrity and confidentiality of your files is guaranteed by mathematics computed on the client side, and is independent of the servers, which may be owned and operated by someone else. To learn more, read [our one-page explanation]source:docs/about.rst.
A2: Tahoe-LAFS provides reliable, fault-tolerant storage. Even if you do not need its security properties, you might want to use Tahoe-LAFS for extremely reliable storage. (Tahoe-LAFS's security features do a good job of staying out of your way when you don't need them.)
@ -32,7 +32,7 @@ A: There isn't currently a way to disable the encryption, but if you look at the
**<a name="Q4_where_are_the_docs">Q4:</a> Where should I look for current documentation about the Tahoe-LAFS protocols?**
A: [<https://tahoe-lafs.org/trac/tahoe-lafs/browser/docs/architecture.rst>]source:git/docs/architecture.rst
A: [<https://tahoe-lafs.org/trac/tahoe-lafs/browser/docs/architecture.rst>]source:docs/architecture.rst
**<a name="Q5_embedded_devices">Q5:</a> Does Tahoe-LAFS work on embedded devices such as a [PogoPlug](http://www.pogoplug.com) or an [OpenWRT](http://openwrt.org) router?**
@ -42,11 +42,11 @@ If you try it, note that the Tahoe-LAFS storage *server* is a much less demandin
**<a name="Q6_windows">Q6:</a> Does Tahoe-LAFS work on Windows?**
A: Yes. Follow [the standard quickstart instructions]source:git/docs/quickstart.rst to get Tahoe-LAFS running on Windows. (There was also an "Allmydata Windows client", but that is not actively maintained at the moment, and relied on some components that are not open-source.)
A: Yes. Follow [the standard quickstart instructions]source:docs/quickstart.rst to get Tahoe-LAFS running on Windows. (There was also an "Allmydata Windows client", but that is not actively maintained at the moment, and relied on some components that are not open-source.)
**<a name="Q7_mac_os_x">Q7:</a> Does Tahoe-LAFS work on Mac OS X?**
A: Yes. Follow [the standard quickstart instructions]source:git/docs/quickstart.rst on Mac OS X and it will result in a working command-line tool on Mac OS X just as it does on other Unixes.
A: Yes. Follow [the standard quickstart instructions]source:docs/quickstart.rst on Mac OS X and it will result in a working command-line tool on Mac OS X just as it does on other Unixes.
**<a name="Q8_storage_in_multiple_dirs">Q8:</a> Can there be more than one storage directory on a storage node? So if a storage server contains 3 drives without RAID, can it use all 3 for storage?**
@ -117,7 +117,7 @@ A: For immutable files this is true—the resulting capability will be the same
**<a name="Q15.1_dedupe_dangers">Q15.1:</a> Isn't deduplication dangerous? Can someone figure out whether or not I have a certain file?**
A: It is dangerous, even more so than most people realize! But, Tahoe-LAFS provides a defense: source:git/docs/convergence-secret.rst.
A: It is dangerous, even more so than most people realize! But, Tahoe-LAFS provides a defense: source:docs/convergence-secret.rst.
**<a name="Q16_move_node_to_different_machine">Q16:</a> If I move the client node base directory to different machine and start the client there, will the node have the same node ID as on the previous machine?**
@ -133,7 +133,7 @@ A: Faruque Sarker has been working on this as a Google Summer of Code project. H
A: Tahoe-LAFS is designed to be unobtrusive. First of all, it doesn't start at all except when you tell it to—you start it with `tahoe start` and stop it with `tahoe stop`. Secondly, the software doesn't act as a server unless you configure it to do so—it isn't like peer-to-peer software which automatically acts as a server as well as a client. Thirdly, the client doesn't do anything except in response to the user starting an upload or a download—it doesn't do anything automatically or in the background (this might change in future, to support background repair for example, but probably only if you explicitly enable it). Fourthly, with two minor exceptions described below, the server doesn't do anything either, except in response to clients doing uploads or downloads. Finally, even when the server is actively serving clients it isn't too intensive of a process. It uses between 40 and 56 MB of RAM on a 64-bit Linux server. We used to run eight of them on a single-core 2 GHz Opteron and had plenty of CPU to spare, so it isn't too CPU intensive.
The two minor exceptions are that the server periodically inspects all of the ciphertext that it is storing on behalf of clients. It is configured to do this "in the background", by doing it only for a second at a time and waiting for a few seconds in between each step. The intent is that this will not noticably impact other users of the same server. For all the details about when these background processes run and what they do, read the documentation in XXX [storage/crawler.py]source:git/src/allmydata/storage/crawler.py?annotate=blame&rev=3cb99364e6a83d0064d2838a0c470278903e19ac and [storage/expirer.py]source:git/src/allmydata/storage/expirer.py?annotate=blame&rev=e76092e16c64019857441e9020d6d8ba2bdaa0bc.
The two minor exceptions are that the server periodically inspects all of the ciphertext that it is storing on behalf of clients. It is configured to do this "in the background", by doing it only for a second at a time and waiting for a few seconds in between each step. The intent is that this will not noticably impact other users of the same server. For all the details about when these background processes run and what they do, read the documentation in XXX [storage/crawler.py]source:src/allmydata/storage/crawler.py?annotate=blame&rev=3cb99364e6a83d0064d2838a0c470278903e19ac and [storage/expirer.py]source:src/allmydata/storage/expirer.py?annotate=blame&rev=e76092e16c64019857441e9020d6d8ba2bdaa0bc.
**<a name="Q19_repair">Q19:</a> If a storage server dies and new one is installed, will Tahoe-LAFS automatically generate a new share of each file to store on the new one?**
@ -156,7 +156,7 @@ Ideally, all clients attempt to open connections to all servers, and all server
**<a name="Q22_literalcaps">Q22:</a> What are literal caps?**
A:
Literal caps (or LIT caps) are simply the base32 encoding of the file data, and are used for very small files. The threshold is 55 bytes (source: XXX [immutable/upload.py]source:git/src/allmydata/immutable/upload.py?annotate=blame&rev=196bd583b6c4959c60d3f73cdcefc9edda6a38ae#L1504), which is
Literal caps (or LIT caps) are simply the base32 encoding of the file data, and are used for very small files. The threshold is 55 bytes (source: XXX [immutable/upload.py]source:src/allmydata/immutable/upload.py?annotate=blame&rev=196bd583b6c4959c60d3f73cdcefc9edda6a38ae#L1504), which is
the break-even point at which the LIT filecap is the same length as a typical CHK filecap. They are sufficient (you don't even need network access to turn the LIT filecap into the data), and necessary (if you don't know the filecap for my data, you can't figure out the data). See this mailing list thread:
* [*pipermail/tahoe-dev/2010-April/004235.html Storing a small file leads to a weird read capability] (especially [*pipermail/tahoe-dev/2010-April/004237.html this message by Brian Warner])
@ -165,7 +165,7 @@ Literal caps are supported for immutable files and immutable directories (see [t
**<a name="Q23_FUSE">Q23:</a> Can I access files stored in Tahoe-LAFS via FUSE?**
A:
Yes. Tahoe-LAFS comes with an [SFTP server]source:git/docs/frontends/FTP-and-SFTP.rst. If you point [sshfs](http://fuse.sourceforge.net/sshfs.html) at the SFTP server then you have access to Tahoe-LAFS through FUSE. Alternately, [pyfilesystem](pyFilesystem) interfaces directly with Tahoe-LAFS through the latter's [WAPI]source:git/docs/frontends/webapi.rst and provides both FUSE and Microsoft Windows filesystem access. See #1353 for discussion of possible improvements to FUSE integration.
Yes. Tahoe-LAFS comes with an [SFTP server]source:docs/frontends/FTP-and-SFTP.rst. If you point [sshfs](http://fuse.sourceforge.net/sshfs.html) at the SFTP server then you have access to Tahoe-LAFS through FUSE. Alternately, [pyfilesystem](pyFilesystem) interfaces directly with Tahoe-LAFS through the latter's [web-API]source:docs/frontends/webapi.rst and provides both FUSE and Microsoft Windows filesystem access. See #1353 for discussion of possible improvements to FUSE integration.
There could be performance problems with the FUSE interface if the apps that are using the filesystem use it in a way that doesn't fit Tahoe-LAFS's semantics, and the FUSE layer is required to make many copies of entire files in order to emulate the desired semantics. See [Zooko's post to freedombox-discuss](http://lists.alioth.debian.org/pipermail/freedombox-discuss/2011-November/003162.html) and [Zooko's post to Google+](https://plus.google.com/108313527900507320366/posts/ZrgdgLhV3NG).