Coda File System

Re: General Coda Question.

From: <jaharkes_at_cs.cmu.edu>
Date: Fri, 12 Nov 1999 16:36:00 -0500
On Fri, Nov 12, 1999 at 04:28:02PM +0100, Jan Hinterkopf wrote:
> Hi Folks !
>
> I have a general Coda Question : 
> First my problem : 
> In the moment our Company is locadet in 2 Countrys : USA and Germany.
> On both sides we have Linux servers connected to the Internet ( in USA with a
> leased line, in Germany over Dialup connection.)

Hi Jan,

I don't think Coda is an appropriate solution for your problem.

Coda provides no locking mechanism, and relies on the fact that write-write
sharing is uncommon for many applications. This is very useful in the case of
disconnected operation.

I assume your database files are big binary blobs, so any update will force
the whole file to be refetched, and many WinXX programs like to `lock' files
by writing timestamps or something in them, causing useless conflicts even on
innocent read-only traffic.

> I know i can syncronise the files with rsync for example. But I need
> replicated Volume so people in the USA and in Germany can safetly READ and
> Write on the same data in the USA ( filelocking is very important(Filebased
> Database)).And I donīt want to transfer the whole Database throught the
> Internet for a single entry in Peachtree ( this takes over an half an hour ).

Is that half hour using rsync? You really need file locking if you want to
have RW access on both sites.

> Is this possible with Coda ?

No.

> Has Coda an encryption for the Datatransfer ?
> When not , can i use coda with ssh ?

I won't use the word encryption, it is currently nothing more than XOR
encoding. Coda traffic is UDP based, routing it through an ipsec tunnel would
probably work.

> Can Samba access on an Coda volume (For the WinClients )?

Yes, a Unix-based Coda client can export the volume as a Samba share, or
through NFS.

> Does Coda transfers much Data through the internet when the Data is
> Replicated already and the people are working ?

A server replication is for high availability reasons, they should during
normal operation have a good network connection. Short term disconnections or
network partitions can overall get resolved successfully, but the
server-server replication mechanisms are really designed towards long term
disconnections and weakly connected operation.

The Coda clients are specialized in disconnected and weakly connected
operation. There many are potential conflict cases during reintegration, but
these reintegration cases are in many ways simpler than full blown resolution
between multiple read-write server replicas.

> And last but not least : It is stable enough for this job ??? Or there
> alternatives ?

There probably are no reliable solutions available. With some sort of a
`locking protocol', the best solution probably involves running rsync once
in a while. As far as the locking protocol... Germany gets R/W access from
8:00 to 15:00 (CET), and the US has R/W access from 10:15 to 17:00 (PST), the
rsync cronjob would first sync only Germany->US (forcing any people violating
the `lock' in the US to lose their updates), and switch over in the other
direction when the US gets the write permission.

If the network bandwidth is good enough, the wallclocks are reasonably in
sync, and people twisted enough, this could be 25minutes Ger, 5minute sync,
25minutes US, 5minute sync, ... However, beware of the daylight savings time
changes.

> Thank you for reading ( maybe understanding) my bad english....

Kein problem,

    Jan
Received on 1999-11-12 16:39:17