Storage IOPs Calculation for Qmail Server

[Gedalya]

On 11/18/2014 07:31 AM, SasiKumar.K wrote:
> Dear DovecotORG,
>
>                  In my organization, we are about to implement Qmail Server.
>
> *  The number of current users will be 800, in future it may increase upto
> 1200.
>
> *  The number of concurrent users will be 300.
>
>   
>
> I am the engineer to deploy the Qmail in Linux server. I need to tell the
> storage team on the IOPs requirement.
>
This is the dovecot mailing list, and your question has nothing to do 
with dovecot. I assume perhaps you're asking here just because there are 
people here who know email. The thing is that the amount of IOPS depends 
a lot on the implementation - you can save IO by using e.g. dovecot's 
mdbox etc.
What do you mean by qmail? Will you use just pop3? No imap? Concurrent 
meaning..? If pop3, connections are very short lived. How will you have 
300 out of 800 connected simultaneously?
It's impossible to actually give you any number, but here are some 
guidelines.
IOPS is primarily a number of writes. If you use tons of RAM you can 
make IO read operations a rare event (like once per minute, on your 
scale, is quite possible).
As for writes, they happen when a new email is delivered, and when it is 
flagged or deleted.
That's about it. It's not a direct function of how many users you have, 
but rather how many messages pass through your server per day.
My rough guess is that 6 3.5" drives might be sufficient for you if you 
process, say <= 100,000 messages per day.