are cutsiepop and sendmail two of programs that you refer to as "non c-type applications"
By "cutsiepop", do you mean cucipop? "C-type" doesn't make any sense (they're written in C, but who cares). Do you mean "c-client type"?
Neither cucipop or sendmail are c-client applications, in that they do not use the c-client library to do their thing. However, they are constrained by the same locking limitations that any server using Unix-file-format mailboxes is.
Of course, any program using maildir-format mail spools is capable of functioning without locking; however, there is a performance penalty, or a correctness penalty, or both.*
When you say each user gets a separate server do you mean each individual account? and by server do you mean server application or complete server hardware?
I'm wondering about Mark's answer here. Mark's answer implied to me that each user had his own server. I do not believe that's the case. Many users might share a server, but the server is always referred to by a user's own name in DNS, as Mark described. This provides a way of moving a user without his client being aware of it. I like this method; it's cute, and solves a lot of the problems without a hell of a lot of work. (I've never tried it personally, though.)
I'm also not familiar with Lustre, either. I will note that it looks promising, but young. However, Mark's criticisms are correct. You are attempting to increase the scalability and reliability of an I/O bound service by adding more CPU and increasing the net amount of I/O done per operation.
Tim
* Single-file-per-message works well enough without locking, but searching must be slow if there are no indexes, because that's a lot of filesystem access. The very cursory demonstrations of maildir caching that I've seen improve things, but must break down under heavy load, particularly concurrent access. Cyrus does single-file-per-message, but since it has locking, it can do good indexing. Searches can be quite quick, depending on configuration, and reportedly REAL FAST if the "squat" stuff is enabled. This isn't very relevant to this discussion but probably will be the next time the archives get searched.
