Coda File System

Coda & InterMezzo

From: Jan Harkes <>
Date: Fri, 21 Sep 2001 15:11:10 -0400
On Fri, Sep 21, 2001 at 11:09:33AM +0800, Xuefeng wrote:
> I am wondering how is the Coda project now. Is it still an actively
> participated Open-source project among Internet community?

There definitely is a community of active Coda users, I don't know about
the Internet community in general, Coda has it's unique niche among
network and distributed file systems and most people out there probably
don't have a want or direct need for Coda's features.

The kernel part of Coda is also used by several other projects as a
convenient and reasonably portable way of implementing UserFS type file

> How does it compare with other open-source DFS projects, such as
> Intermezzo and others?

Coda doesn't use perl for the userspace cache-manager. No really,
InterMezzo is the brain-child of Peter Braam, who was the Coda project
leader for several years. It's goals were to provide 90% of the Coda
functionality in 10% of the code. The goal has I believe shifted a bit
more towards providing a reliable filesystem for clusters, although that
might be another project Peter has been working on.

I haven't played with InterMezzo myself, so I can't really tell you what
features is does or doesn't have. However, it should be quite a bit
faster, because it's kernel module is designed to really minimize the
number of upcalls to userspace by among others keeping a log of write
operations at the kernel level and the kernel manages access to the
cached files instead of the userspace manager. Upcalls require at least
2 context switches so they are typically quite expensive and these
design differences should vastly improve InterMezzo's performance on
directory operations and file opens/closes.

Actual file read/write performance (once the file is opened) should be
the same for both Coda and InterMezzo as both redirect these operations
directory to the cached files without having to make upcalls to
userspace. This btw. is also the reason why Coda doesn't support a hard
cache size limit, we only get to see the size of the file after the
application is done writing and closes the file.

Received on 2001-09-21 15:14:33