The Register published an article describing the removal of Single Instance Storage (SIS) from the Exchange Server 2010 database engine.  The comments on the article were largely critical of the change, declaring it a backward step in Exchange storage efficiency.

Before I discuss this further it helps to go back in time a little and understand what SIS is and how it came to be a part of Exchange Server.

Exchange Server Single Instance Storage

The essence of SIS is the storage of a single copy of data that is shared among different users or computers.  In the case of Exchange Server this meant a single copy of an email or file attachment is kept in the mailbox database, and then any user who received that item accesses it via a pointer to that one single instance of the item.

SIS was introduced in the Exchange Server product line in version 4.0 back in 1996.  Back then disk storage was very expensive compared to today’s prices.  Disks were much larger in physical size, smaller in capacity, and slower in performance.  Under those conditions SIS made a lot of sense to reduce the overall size of mailbox databases.

SIS remained a part of the Exchange database engine right up to Exchange Server 2007.  However in this time the price of disk storage has greatly reduced.  The database engine itself had also been improved and between Exchange Server 2003 and 2007 saw as much as a 70% decrease in IOPS (Inputs/Outputs per Second) requirements, meaning more users and larger databases could be stored on fewer disks. Continue reading Does the Removal of Single Instance Storage Mean Less Efficient Exchange Servers?

In my recent post I examined the question of whether Exchange Server 2010’s new replication and retention features could mean an organization no longer needed to back up their Exchange servers.

One reader emailed me to suggest that avoiding backups would be unwise, citing the example of potential corruption within the database that might replicate to all copies within the Database Availability Group and cause loss of data.

The scenario is one that definitely needs to be considered.  Although Exchange Server 2010 includes application intelligence to detect and handle some database corruption scenarios, there still exists the possibility of logical corruption leading to data loss.

Fortunately the solution to this problem is already included in the DAG feature of Exchange Server 2010.

If you are already familiar with Exchange Server 2007 Standby Continuous Replication then you already understand the concept of replay lag time.  Replay lag time is a configurable setting on each database copy within a DAG that delays the replay of a transaction log into that database replica.  A database copy with a replay lag time of more than zero is referred to as a lagged copy.

For example, within a DAG there may be 3 servers hosting replicas of Database 1.  Two of the servers are located in a primary data center, and the third server is located at a secondary data center.

The servers at the primary data center are configured with a replay lag time of zero, meaning the passive copy of the database is kept up to date with the latest transaction log information in near real-time.  A failure of one server permits seamless failover to the second server and continued email operation for the business. Continue reading What if You Never Backed Up Your Exchange Server Again? (Part 2)

Imagine for a moment that you never had to back up your Exchange servers again.  Sounds crazy right?  Well with Exchange Server 2010, it may not be as crazy as you think.

In a recent post I described the killer new High Availability feature of Exchange Server 2010 – the Database Availability Group (or DAG for short).

A DAG is an Organization-level object that allows a database to have several passive replicas on other servers (DAG members).  When a DAG is configured it permits individual mailbox databases to failover to passive instances should any problem with the active database arise.

The nature of DAGs means that they can be deployed to protect from failures at almost any layer of the Exchange infrastructure.  DAGs can protect from anything from a single failed server hard disk to an entire data center failure as long as the DAG is architected accordingly.

How this relates to backups is simply this – if a database is protected from all failure scenarios by the DAG, why would you need to back it up at all?  Let’s take a closer look at this question. Continue reading What if You Never Backed Up Your Exchange Server Again?

I recently wrote a five part series about Exchange Server 2007 high availability, describing each of the HA features (LCR, SCC, CCR, and SCR) in detail and demonstrating their uses, strengths and weaknesses.

With the release of Exchange Server 2010 these high availability features are no longer available.  The features have now been replaced by a single high availability option known as Database Availability Groups (or DAGs for short, admittedly a horrible acronym for what is truly the product’s finest feature).

A little background is required to fully understand the evolution of Exchange storage architecture to its current incarnation in DAGs.  Going back to Exchange Server 2003 the product was limited to a maximum of 4 Storage Groups, each containing a maximum of 5 databases.  This meant a maximum of 20 databases (of either Mailbox or Public Folder type) per Exchange server.

Exchange Server 2007 improved on this in two ways.  Firstly, the product was limited to 5 Storage Groups and 5 databases for the Standard Edition, and up to 50 Storage Groups and databases for the Enterprise Edition.  The best practice with Exchange Server 2007 was to use one Storage Group per database, unlike Exchange Server 2003.

Naturally this lead to the question of why have Storage Groups at all?  Exchange Server 2010 answers this question by doing away with the concept of Storage Groups entirely.  Databases are now Organization-level objects that contain both the transaction logs and the database itself.

Exchange Server 2010 then introduces the Database Availability Group to provide high availability.  A DAG is a group of Mailbox Servers (up to 16 per DAG) that replicate databases and perform automatic failover and recovery for either individual database or entire server failures.

So how does this compare to Exchange Server 2007 high availability?  An immediate advantage is that DAGs unify Exchange high availability into a single feature and management toolset, unlike Exchange Server 2007 which had 4 different features each managed with different tools.

Let’s take a more detailed look at each of the features to see how they compare to DAGs. Continue reading Exchange Server 2010 Delivers Improved Availability