I look after several clients with on premise Exchange Servers. Most clients are relatively small but I have one that has grown quite considerably in the last 12 months and they now have 150 mailboxes on a single Exchange Server. The mailboxes have a combined size of 250GB and are spread over 5 databases.
Its a Exchange 2013 (SP1) Server and is running virtually (HyperV). The Physical host is a Dell Powerdge R710 with 6x 600GB 15k SAS disks in RAID 5.
The Exchange VM has 16GB of RAM and 8 CPU's allocated to it. The databases are stored physically on the RAID 5 disk set using two different virtual disks.
The issue Im having is the client is reporting Exchange Freezing a random times during the day. The Exchange Server was originally pretty quick but has slowed down as more users have been added to it. The client reports the freezing occurs multiple times every hours and lasts for 10secs+ each time.
My question is this - given the above setup, how many users should I be expecting to run comfortably off this Exchange 2013 Server?
At what point typically would you consider adding another Exchange Server? I haven't tried any performance tweaks (other than sprading the load overe several databases), its a stock install. I know its good to have a second Exchange Server for redundancy (so I will be probably adding a second one anyway) - but based purely on performance considerations, is there a magic number of mailboxes you can typically get working off a single Exchange 2013 Server?
I tried to use the Excel calculators provided by MS, but they seem to be suited more towards companies with bigger user bases.
The client is also not interested in Office 365 because they want to keep all their data in house.