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Microsoft nixes SIS in Exchange Server 2010

In order to lower I/O and improve Exchange Server 2010 performance, Microsoft removed single instance storage. How will this affect messaging environments?

Microsoft removed single instance storage in Exchange Server 2010 in favor of new architecture and database compression technology -- a change that may affect storage requirements and how IT pros manage their messaging environments.

Instead of single instance storage (SIS), Exchange Server 2010 uses database compression technology and new tools that help administrators purge mailboxes and keep database sizes down. But when Microsoft de-emphasized SIS in Exchange Server 2007 last year, heads turned; and many Exchange users have been sounding off about the loss of SIS on TechNet.

Microsoft downplayed the impact on its Exchange blog site this week, but admits that there are instances where not having SIS will pose problems. For example, environments that only send rich text format (RTF) messages will experience a storage strain because the compression algorithms Microsoft uses in place of SIS to keep database size down do not compress RTF messages.

Not having SIS also creates a problem when sending large attachments to 20 or more users located on the same store. With SIS, for instance, if only five recipients out of the 20 on the same database received a 30 MB attachment, the attachment was stored once instead of five times. But in Exchange 2010, that attachment is stored five times -- totaling 150 MB -- and it isn't compressed, according to Microsoft.

Those scenarios are cause for alarm, said Richard Ayars, executive vice president at the Arlington, TX-based IT services company Custom Information Services.

"What happens when a user sends a 20 MB attachment to everybody in the mail store; a single message could eat up 20 GB of storage," Ayars said. "This [change] will force IT managers to train their users to follow sound practices when using email and create a need for more administration of the mail stores."

Microsoft's evolution from SIS
SIS was originally built into Exchange version 4.0 in 1996 to lower storage requirements at a time when storage costs were much higher. The idea behind SIS is that when a user sends a message out to numerous people with mailboxes in the same store, the original message is stored once instead of many times, and recipients access one stored message.

But storage costs are at an all time low and the use of multiple mailbox databases in Exchange Server, which don't benefit from SIS because it only works within a single database, have made the method far less important, said Rob Sanfilippo, an analyst with the Kirkland, Wash.-based analyst firm Directions on Microsoft.

"Microsoft has redesigned the Exchange store schema to decrease disk I/O and increase performance, and it was apparently more efficient to eliminate SIS in the process," Sanfilippo said.

The impact
Exchange users who "cling to the past" and build Exchange environments the same way they did with Exchange Server 2003 and earlier will most feel the effects of this change. For them, storage costs will be higher than they have to be, said Michael Crowley, a messaging administrator who builds Exchange environments for Germantown, Md.-based Planet Technologies Inc.

Also, shops with only a few Exchange servers will see a database size increase, and will need larger disks and larger backup systems, Crowley said.

But Exchange 2010 better supports inexpensive Direct Attached Storage (DAS) drives through its reduced I/O overhead, which could circumvent the cost of buying extra storage, Sanfilippo said.

"Additional storage will be something for IT shops to consider if they are adopting Exchange 2010's server-based personal archive mailboxes, so the elimination of SIS won't be the only reason for more storage," Sanfilippo said.

Andre Preoteasa, IT director for New York-based alcoholic beverage provider Castle Brands Inc., said having larger mailboxes and other advantages in Exchange 2010 offset not having SIS, especially since hard drives are relatively inexpensive.

"If the internals of storing mail had to change, then so be it," Preoteasa said. "But hopefully Microsoft's mailbox database stores do not start massively increasing."

Sanfilippo said storing large files outside of Exchange on a SharePoint site, for instance, will reduce any noticeable impact in storage costs and requirements for Exchange deployments. Crowley said concerns about losing SIS are "mostly unwarranted," and suggests that enterprises follow Microsoft's direction to keep storage costs down.

"If people take a bit of a leap and follow Microsoft's new storage design guidance, they will actually realize a huge reduction in disk cost. The removal of SIS was accompanied by the introduction of Database Availability Groups, which [when used] in three-plus server deployments, do not even require RAID disk subsystems," Crowley added.

Let us know what you think about the story; email Bridget Botelho, News Writer and follow @BridgetBotelho on Twitter.

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