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Email has become an integral part of business processes. Every day
business is conducted, customers are contacted, information is relayed
through email.
- Requirements
-
Our customer is a import/export broker. Shipment inventories for which
they prepare documents are emailed several times a day, while fewer
documents are received through traditional methods like mail, faxes
and courier delivery. After a recent massive failure of their previous
system, where email was unavailable for a whole day, the customer
decided it was time to look for other options.
Our customer was very specific about their requirements. They wanted
a highly reliable system. The system needs to always be up, except
for the rare power outage that exceeds the ability of a UPS to keep
the servers running. In other words a high availability system. Since
the customer relies heavily on email to get information from their
customers, the system must have zero downtime and must not lose mail.
In case there was a hardware failure there must be a minimal time
to get the broken hardware back on line. And the cost must be competitive
with the three year costs of an outsourced solution.
- Options
-
We looked at several possible options.
- Microsoft Exchange Server
-
Microsoft calls their solution a cluster. It seems to me to be primarily
a load sharing rather than a high-availability solution. It requires
some kind of shared media, probably fibre-channel raid. Control is
passed by way of locks on the file system and a communication mechanism
that notifies other members of the cluster which system has operational
control over the data. We estimated that the software and hardware
costs would exceed $58K, before any setup fees.
- Mail Server with shared media
-
Similar to the Microsoft solution this depends upon fibre-channel
shared media. HBA cards run about $1000 each and since we were using
three servers this would increase the cost for three servers from
$12,000 to $15,000 and a fibre-channel storage solutions would add
about another $9K, bringing the hardware costs to about $25K. This
would have made the cost non-competitive with an outsourced solution.
- Mail Server with mirrored drives
-
The more cost-effective solution seemed to be network mirrored drives,
using DRBD. According to the DRBD web site, ``DRBD is a block device
which is designed to build high availability clusters. This is done
by mirroring a whole block device via (a dedicated) network. You could
see it as a network raid-1.''
``DRBD is designed to work with High-availability Linux to provide
redundancy and fail-over.''
Using Mondo Rescue http://www.microwerks.net/hugo/
we could do a bare metal re-install on a third server for quick recovery
of failed hardware.
This seemed like the most cost effective solution.
Next: The setup
Up: High Availability Mail Server
Previous: High Availability Mail Server
