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Distributed Filesystems for Linux?
Zoneball looked at 3 distributed filesystems, here are his thoughts:
" Open AFS was the solution I chose because I have the experience with it from college. For performance, AFS was built with an intelligent client-side cache, but did not support network disconnects nicely. But there are other alternatives out there.
Coda appears to be a research fork from an earlier version of AFS. Coda supports disconnected operations. But, the consensus on the Usenet (when I looked into filesystems a while ago) was that Coda was still too 'experimental.'
Intermezzo looks like it was started with the lessons learned from Coda, but (again from Usenet) people have said that it is still too unstable and it crashes their servers. The last 'news' on their site is dated almost a year ago, so I don't even know if it's being developed or not"
So if you were to recommend a distributed filesystem for Linux machines, would you choose one of the three filesystems listed here, or something else entirely?
I would use SFS, the Self Certifying File System. Assuming all the systems you are using are supported, it offers global, secure access to anything you care to export.
Since openafs forked from the old transarc/IBM codebase, it looks as if it has a real future. It's used by a load of educational and research institutions (notably CERN), as well as Wall Street firms.
Check here for a good background on DFS. It also has a quick table comparison of the popular programs, and a walkthrough to set up Intermezzo.
We use PVFS at work to give us a high-performance network filesystem for use with our clusters.
http://parlweb.parl.clemson.edu/pvfs/
I run an openmosix cluster with the openmosix filesystem here at work. Three computers.. no problems...
If you want to take a look..
http://lucifer.intercosmos.net/index.php
linkage and I am going to be placing some tutorials up. -joeldg
anime+manga together at last.. in real time.
While there is no new news posted on the site, ther are current tarballs on the ftp server, as recent as 5.9.03. (but that file appears to be a redux, last update to code seems to be 3.13.03)
The sourceforge page for the project (http://sourceforge.net/projects/intermezzo) shows status as production/stable but the info there looks stale too.
Just so you all know. NFS is a network accessible FS. A DFS can also be network accessible from clients, but it physically resides on multiple systems.
I just went through this process a few weeks ago and I must say I'm really glad I went through the trouble of setting it up...it's very cool. I actually wrote a tutorial about how to accomplish this by using NIS and NFS. I hope you find it helpful.
The only trouble you might run into with the setup I used is some file-locking issues with programs wanting to share the same preference files.
--It's Pimptastic!--
I had more or less the same basic requirements and I opted for AFS.
:DFS, DCOM, Directory Services, SSO, DCE-RPC, etc.)
My needs were a little more demanding (had to be implemented in GNU/Linux, Solaris, AIX, HP-UX and as an extra Windows 2000) and grocking AFS can be difficult at first but it was the best choice by far. Stable across all the Unices, very secure (this was another requirement) and integrates perfectly with our Kerberos Domain and LDAP accounting info. It provides a unique namespace that can span multiple servers transparently, does replication, automatic backups and read-only copies, client-side cache with callbacks, has a backup (to tape) system that can be used stand-alone or integrated with existing backup structures (Amanda, Legato, TSM) AND was the basis for the DCE filesystem, DFS (as a side note I find it interesting - and sad - that most things people try to emulate this days are present in DCE , and Windows 2000 got many of the "new features" from a technology initially made for Unix
AFS is amazing and much more robust than any distributed filesystem I know of; it has shortcomings when servers time out, but apart from that it's really an excellent solution; an example I generally use to give an idea of some of the good features of AFS is a relocation of a home directory to another server. The user doesn't even notice that his home directory was moved to another server *even if he was using it and was writing stuff to disk*; at most all writing calls to his home dir have a small delay (a couple of seconds) even if his/her home dir was 5 Gb worth.
Kerberos integration is an added bonus, if you can you can use this as an excuse to kerberize your systems and form a Kerberos Domain. If you don't want to just stick with the standard AFS KA server.
In my setup I have Windows users accessing their home dirs in AFS using the Kerberos tickets they have from the Windows login and the fact that a cross-realm trust was made between the Unix DOmain and the AD; the can edit all the files they are entitled to with that ticket, and the system is so secure that Transarc used to put the source code in it's public AFS share and added the customers that bought the source to the ACL of the directory that contained it.
With all this features it would be hard not to vivedly recommend OpenAFS as the best solution for a unified, distributed filesystem. Bandwidth utilization is, in my experience, at least half of what NFS uses, which is an added bonus.
cheers,
fsmunoz
Why not stick with NFS for the time being?
I went through the "is coda right for me?" phase, and also "is intermezzo right for me?" and also spent tens of hours researching distributed filesystems and cluster filesystems online ... my conclusion
is that the area is still immature, I will let the pot simmer for a
few more years (hopefully not many), and use NFS in the meantime.
My situation: desire for scalable and fault-tolerant distributed filesystem for home use with minimal maintenance or balancing effort. Emphasis on scalable, I want to be able to grow the filesystem essentially without limit. I also don't want to spend much time moving data between partitions. And last but not least, the bigger the filesystem grows, the less able I will be to back it up properly. I want redundancy so that if a disk dies the data is mirrored onto another disk, or if a server dies then the clients can continue to access the filesystem through another server.
All that seems to be quite a tall order. I checked out coda, afs, PVCS, sgi's xfs, frangipani, petal, nfs, intermezzo, berkeley's xfs, jfs, Sistina's gfs and some project Microsoft is doing to build a serverless filesystem based on a no-trust paradigm (that's quite unusual for Microsoft!).
Berkeley's xFS (now.cs.berkeley.edu) sounded the most promising but it appears to be a defunct project, as their website has been dead ever since I learned of it, and I expect the team never took it beyond the "research" stage into "let's GPL this and transform it into a robust production environment". Frangipani sounds interesting also, and maybe a little more alive than xFS.
On the other hand coda, afs and intermezzo are all in active development. afs IMHO suffered from kerberitis, i.e. once you start using kerberos it invades everything and it has lots of problems (which I read about on the openAFS list every day). AFS doesn't support live replication (replication is done in a batch sense) either.
CODA doesn't scale and doesn't have expected filesystem functionality: for 80 gigs of server space I would require 3.2 gigs of virtual memory, and there's a limit to the size of a CODA directory (256k) which isn't seen in ordinary filesystems. There's also the full-file-download "feature". CODA is good for serving small filesystems to frequently disconnected clients but it is not good for serving the gigabyte AVIs which I want to share with my family.
Intermezzo is a lot more lightweight than CODA and will scale a lot better, but it's still a mirroring system rather than a network filesystem. I might use that to mirror my remote server where I just want to keep the data replicated and have write access on both the server and the client, but it's again not a solution for my situation.
The best thing about intermezzo is that it sits on top of a regular filesystem, so if you lose intermezzo the data is still safe in the underlying filesystem. CODA creates its own filesystem within files on a regular filesystem, and if you lose CODA then the data is trapped.
Frangipani is based on sharing data blocks, so like NFS it should be suitable for distributing files of arbitrary size. I need to look at it in a lot more detail; this is probably the right way to build a cluster filesystem for the long haul. For the short term, Intermezzo is probably the right way for a lot of people: it copies files from place to place on top of existing filesystems.
What I did in the end:
The way it works is tha
I use a very simple script to help keep NFS secure:
Basically it only allows incoming NFS-related connections over ipsec, dropping anything that is not. NFS port allocation is dynamic by default and I know you can force ports, but this seemed far easier to scale.
One thing I have noticed (and perhaps it's common knowledge to NFS experts) is that in order to get locking to work at all, my NFS clients had to be running statd and lockd. Without 'em everything worked but locking would fail every time.