Coda File System

Re: is coda right for me? (mail servers)

From: Jerry Amundson <>
Date: Mon, 11 Oct 2004 11:24:47 -0500
On Monday 11 October 2004 02:13 am, Ivan Popov wrote:
> Hello Jerry,

Hello, and thanks for the quick response.

> > Site 1                                      Site 2
> > ------                                      ------
> > MTA gateway                                 MTA gateway
> > (and coda client)                           (and coda client)
> >
> >
> > MTA server                                  MTA server
> > (coda client     / coda volume(s) for \     (coda client
> >    and           |                    |      and
> > coda server)     \ maildir storage    /     coda server)
> (unclear for me why you need a Coda client on both MTA gateway and
> MTA server? Which protocol is used between them?)

The MTA gateways will do their own local delivery, so will be writing 
maildir files directly to the Coda volume. 

> I can not answer your main question, but want to provide some input.
> One misconception about Coda is that it is optimized for
> distantly placed servers, it is not.

I have not viewed the source, but would it be overly complex to apply 
zlib, or other compression scheme, to the data stream?

> When clients become weakly connected (which means talk to just one of
> the servers) - and this is the normal mode of operation,
> there will be more traffic between the servers than between the
> clients and the servers.
> If your line can bear with the excessive traffic, you are fine,
> and you are protected against one server going down for short
> periods of time, or the line breaking - again, for
> short periods of time. You can not afford running longer in "reduced
> mode", the server logs will eventually fill up and you will loose
> consistency.

Of course we would want such link-breakage periods, if ever, to be 
minimal - hours at most.

Is there a function that we could apply to calculate log size, e.g. for 
(X amount maximum disconnected server time) and (Y expected amount of 
data) - allocate at least Z size log?

> > Q1: Can T1 speed adequately support two Coda servers?
> Is it adequate for at least twice your mail traffic?


> > Current size of the maildir's is 21 GB, but growth is expected.
> Be aware that you cannot have a single directory bigger than several
> thousand entries (directory size is limited to 256K I think).
> It is probably the biggest concern for maildir-based installations.

That might prevent me from pursuing this - we have several users with 
maildir directories with over 5000 files, and one user each in the 
8000, 9000, and 10000 files ranges.

If the limitation is "directory size", then the size of files needs to 
be considered in conjunction with their numbers, right?

> Be also aware about server file number limit. 21G data should be ok,
> twice as much (in small files) will be probably too much if you do
> not distribute data between several servers.
> > Q2: What are practical size limitations of Coda volumes?
> According to Jan there shouldn't be any, though you probably do not
> want to have huge volumes. I think at least some operations on a
> volume are serialized, so the bigger volumes, the bigger risk for
> delays when client processes wait for each other.
> Hope it helps,
> --
> Ivan

It does, thank you...

Received on 2004-10-11 12:25:34