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RE: Server Specifications

Sanford Whiteman — Wed, 25 Aug 2004 10:41:18 GMT

"Number" of course means "maximum number"--that's the only way it makes sense for capacity modeling. You don't build a server where you can vouch for the _mean_ or _median_ amount of traffic that can be processed!

Number of users is proven to be a useless statistic when you get above the mom-and-pop size. Of course, there are many, many people who build servers without planning at all, and they very often get lucky...but once you start to get technical, you should be accurate, or you may end up officially vouching for systems and are left holding the bag if you were wrong.

--Sandy

RE: Server Specifications

Dmitri Elgin — Wed, 25 Aug 2004 06:44:01 GMT

"the number of incoming and outgoing messages per day" is also a little bit blind

the _maximum_ number of incoming and outgoing messages per day - that's the most truly metric

Since the days are different your traffic may increase at the begining and at the end of business periods (week, month, year)

Although, the number of users may not a give a real picture, but

it may be a good starting point to calculate an average number of messages per day or per hour

and define the upper and lower limits of traffic, since the amount of users is constant value,

instead number of messages per day that may vary.

RE: Server Specifications

Sanford Whiteman — Wed, 25 Aug 2004 03:00:30 GMT

The number of users is not really a relevant metric for sizing a mailserver: it is a blind statistic that doesn't take into account real-world usage and has no generic meaning (though it becomes useful when sizing _additional_ servers at one site expecting the same user types as the first). Rather, the number of incoming and outgoing messages per day, combined with projected use of different client protocols (POP3, IMAP4, IWEBMSG), are the metrics you want to offer.

And disk I/O is the most common performance bottleneck on mailservers, but not disk space: the amount of disk _space_ is only relevant to the number of messages that can be stored on the server at projected points in time, message processing. Rather, it's the _speed_ and _functional partitioning_ of your disk subsystem that is much more relevant: these characteristics will determine how much traffic your mail server can handle. Rules of thumb are that you (a) use as much RAID controller cache as you can afford and (b) dedicate as many spindles to as many of the following independent functions as possible:

- OS

- IMail exes

- SMTP spool

- web spool

- log directory/ies

- virtual host top directory/ies

The more horsepower you can give to these independent and overlapping functions, the less contention there will be for your disk subsystem and the faster it will perform.

As for CPU sizing, it is largely a worry for IMAP4, IWEBMSG, and content filtering (virus or spam). Performance of these functions will improve with faster or multiple processors. On the other hand, the simpler SMTP and POP3 protocols are conservative with CPU.

--Sandy

RE: Server Specifications

gnetwerker — Tue, 24 Aug 2004 18:16:32 GMT

A 1GHz server will be fine. You need to worry more about how much main memory you have, as well as the disk space.

Regarding memory, 256Mb would be a bare minimum, but I wouldn't run with less than 500Mb, and would prefer 1Gb if you expect lots of simultaneous connections. I just checked, and my server is using about 200Mb of physical memory in a more-or-less quiescent state, with all the iMail services running, as well as DNS and the usual Windows services.

Re: disk, this depends a great deal on whether you will offer IMAP services to everyone. If so, you'll either have to police tightly or I would venture that this is too small for 1000 users. POP users will of course leave less lying around, and if you're just forwarding, then no worries at all.

Win2K Server with a swap space and iMail and little else will take about 3Gb or so, leaving you with perhaps 10Gb usable disk space. This leaves an average of 10Mb per user for disk usage. If this is guaranteed-not-to-exceed, then this may work even for IMAP (provided you're not also archiving you mailing lists, backing up to local disk, etc), but hard disks are so cheap I think you'd be very well served (no pun intended) sticking a 50Gb disk in there for $100. After all, how much is your time worth in worrying about the disk space?

Best,
Gnet

Server Specifications

Brian Hegg — Tue, 24 Aug 2004 17:09:53 GMT

Just purchased IMail Server for our membership. My question is this:
What kind of specifications do I need for my server - would like to put on a server we currently own but worried about the space requirements. Initially this will be used for less than 1000 email accounts and about 30 different listserves. The server I would like to put it on has only about 14 GB with WIN2000 and a 1 GHz PIII processor. Is this acceptable or would it be better to upgrade this server - or - buy a new one.

thanks in advance for any help provided.