New server configuration questions

[Jeff]

Hi all, I have been lurking on the list for a while now and decided to take
the plunge.  I am building a new mail server config for work.  

So far, the hardware I have is 2 x Sun 420r's loaded & 2 x a5200 loaded with
18GB drives connected via fibrechannel.  I am planning on building a
completely redundant configuration, with one of the 420's and one a5200 at
one location, with the other set at my location.  I have installed the
fiberchannel extenders (~60KM) and am almost ready to start the hard part
:).

My current setup on my existing mail server is simple.  I use cucipop and
sendmail/procmail. Pretty basic config over all.  I have about 10,000 mail
boxes that consume about 18-20GB of space.

My plan is to have one of the 420's doing all the work.  It will write to
both a5200's.  In the case of hardware failure, the second 420 will take
over from the other pop.

The questions I have are these:

1:  Partitioning?  I would like to have about 200GB available for mail
storage.  I think once we allow our clients to use IMAP, our storage needs
will increase.  We quota each mailbox to 20MB, so at current levels it would
match perfectly.  Should I create separate partitions for the clients,
mqueue and db area's?  Which partition requires the fastest access?

2: Recovery?  Is it difficult to recover from a crashed write from cyrus?
In the event the master server goes haywire and the secondary server takes
over, what kind of time should I allow for cyrus to recover and rebuild the
mailboxes that may be corrupted?

3: Sendmail or Postfix?  I currently use sendmail and I am quite comfortable
with the cf/mc files.  Are there advantages to postfix with this
configuration.  Our current mail load is about half a million incoming
messages a day. A different server handles outgoing mail.

4: any suggestions on what to look out for using this kind of config?

Thanks,

Jeff.

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