(Illustration by Gaich Muramatsu)
On Tue, May 29, 2001 at 03:21:46PM +0200, Mourad De Clerck wrote: > My questions now are: > * do you think cable/adsl is adequate for such an application, > considering the overhead of coda? It is definitely adequate, I myself am using a slow dialup link, but several of the graduate students here at CMU are using Coda over ADSL. They did identify a problem, Coda uses bandwidth estimates to adapt it's behaviour towards available bandwidth. This estimation code is part of RPC2 and currently assumes a symmetric link. However, we effectively have both strong and weak connectivity at the same time (depending on read/write traffic) and wrong decisions are being made about whether to switch into write-disconnected or fully connected mode and how much data should be reintegrated at a given time. > * what happens if a file gets saved again on thesame machine, before the > previous update has finished propagating? (is the file still sent two > times?) When Coda is in write-disconnected mode any modifying operations, such as stores, are kept locally for about 5-10 minutes to allow for optimizations (newer stores overwriting old ones, create/remove cancellations, etc.). But once a file is being propagated and a new store arrives, the store in progress is not aborted. So yes, when the stores are typically more than 5 minutes apart, the file will be sent multiple times. > * should i setup a coda server at each location, or just one at the > "main" server (+ maybe a backup) (the vpn has point-to-point links from > each node to each node) One or two servers in a central location is best, Coda servers like to be "central" with good connectivity. The caches on the clients should provide a good buffer to reduce most network traffic. > * since most of the people work on Mac's i need to get the files on > their desktop somehow too... i thought doing this by sharing the /coda > directory with netatalk. Could this be a problem? Haven't tried this. We have successfully shared /coda using userspace nfsd and samba servers. The main problem is when a conflict is detected during reintegration of the disconnected operations. There is no way for the clients to repair such a problem and they will be denied access to the involved files (or directory tree) until someone on the machine that exports /coda repairs the conflict. > * i've heard that coda doesn't scale so well - is this true? Scalability is relative. A Coda server can currently handle many clients, and lots of data, but not a lot of files, or many files per directory. The limitations that I've seen hit are around 150000-200000 files for every 100MB of configured RVM. Because of 32-bit address space limitations it is not realistic to run a server with more than 1-2GB of RVM, in which case the server would also need at least the same amount of virtual memory (real + swap). Extending this, a Coda server would max out at around 2 million files. Other problems are likely to hit before this time, such as excessively long server-startup times. Directories tend to fill up with as few as 4000 names. > * can i use coda without problems for home directories? (kind of a > "roaming profile") Yes, however some files are continually rewritten in the background by applications and are prone to getting unwanted conflicts as soon as a user would work from different machines. These are best replaced by symlinks to a local disk partition. Examples of these are ~/.netscape/bookmarks, and enlightenment or several gnome application configuration files. > * is there a specific filesystem recommendation for use with coda? > (ext2, reiser, xfs) As far as Coda clients are concerned, ext2 has been used the most and works well. ReiserFS is not supported by anything but recent Linux kernels (2.4.4 and later). I haven't looked at XFS yet, so it could still have problems. For Coda servers life is much better, because the server is a traditional userspace application. Any filesystem will work. > * what happens when there's not a lot (relatively - compared to the > server) of space on the harddrive for the cache? It depends more on what the client's working set is. When the client typically needs 100MB, anything less as a local cache will cause many file refetches. My email folders add up to about 30MB, a smaller cache causes a storm of fetches every 5 minutes when checks for new mail are performed. JanReceived on 2001-05-29 11:22:09