Coda File System

Re: Filesystem replication or expansion

From: Ivan Popov <>
Date: Sun, 31 Aug 2003 15:42:01 +0200 (MEST)
Hello Cyril,

> > the biggest disk space servable by one server is still about 25G.
> I've heard about this problematic limit several months ago but since I
> was not able to find anything about that in the documentation, I
> thought this limit has just gone.

unfortunately according to my understanding this limit is hardwired rather
deep in the implementation, that has been 32-bit-oriented from the
beginning. It looks like Jan has removed many 32-bit dependencies but
still there are some.

>  I think it should appear somewhere
> in the FAQ.

Or finally be solved.

> You can find 250GB hard disks at 350 EUR; this allow you to easily set
> up 1TB servers with 4 disks; the 25GB (0.025TB) Coda limitation might
> seem obsolete nowadays.

Yes it *is* obsolete. On the other side the development focus has been
always on the core functionality - failure resilience, replication and
disconnected operation, the things absent in other filesystems.
As Jan wrote, there are still tricky issues in that area. It is
important to make Coda rock-solid - before tuning it for large

> At that time, I'm interested in distributed filesystems like Coda
> because I need to transparently provide a 320GB networked filesystem
> to 6 clients with two 160GB servers; I also need the ability to extend
> the filesystem size by adding servers, it should grow to 1TB soon.

If your files are rather big, you might do it with Coda.
Coda does not handle well
 - lots of small files (because of rvm size limitation)
 - really big files (as whole file caching can feel slow)
 - concurrent updates (creating conflicts)
but on the other side it is very good at hiding flaky lines and failing
servers, does not waste bandwidth and can be really fast, depending on
your usage pattern.

> with Coda.  Is there a way to raise the limit by tuning block sizes or
> anything else?

Current recipe is to run a lot of server processes, in your case say 6 per
server host (for rather small "typical Unix" files). No big deal for the
functionality, but makes is harder to administer.

> Is there a way to solve my problem with Coda?  With something else?

It depends on your needs. If you do not want disconnected mode and
read-write replication, you may look at OpenAFS.

Received on 2003-08-31 09:45:39