Single instance storage is a feature of Exchange that we haven't talked about much since the 1990s. We made some changes to how single-instancing works in Exchange 2007, so I wanted to give everyone ...
Updated Jul 01, 2019
Version 2.0
Blog Post
Joshua –
Attachment related properties have always been stored in the attachments table. There is no added separation that was added in recent versions. I can’t really comment on what the future database changes or APIs may bring. As far as perfmon counters go, I am pretty sure that the single instance storage ratio is the only SIS related counter.
Adam –
When data is read from the database it goes into the JET cache. If we need to re-read that data we’ll check the cache first in order to avoid going to disk if the data is cached. With Exchange 2003 and below we were limited to having a JET cache of around 900 MB. Because of this we were limited by how much data could be cached and how long it would remain there, meaning that even with SIS there is no guarantee that we only need to read the information from disk once when several users within a short time of each other attempt to open that attachment. Even with the fact that some of the changes that were made in Exchange 2007 caused message bodies to no longer be single instanced, Exchange 2007 does provide a very significant reduction in I/Os. This is due to the advantages we get from 64-bit as well as the other changes described in Chris Mitchell’s previous post: http://msexchangeteam.com/archive/2006/09/08/428860.aspx
-Nick
Attachment related properties have always been stored in the attachments table. There is no added separation that was added in recent versions. I can’t really comment on what the future database changes or APIs may bring. As far as perfmon counters go, I am pretty sure that the single instance storage ratio is the only SIS related counter.
Adam –
When data is read from the database it goes into the JET cache. If we need to re-read that data we’ll check the cache first in order to avoid going to disk if the data is cached. With Exchange 2003 and below we were limited to having a JET cache of around 900 MB. Because of this we were limited by how much data could be cached and how long it would remain there, meaning that even with SIS there is no guarantee that we only need to read the information from disk once when several users within a short time of each other attempt to open that attachment. Even with the fact that some of the changes that were made in Exchange 2007 caused message bodies to no longer be single instanced, Exchange 2007 does provide a very significant reduction in I/Os. This is due to the advantages we get from 64-bit as well as the other changes described in Chris Mitchell’s previous post: http://msexchangeteam.com/archive/2006/09/08/428860.aspx
-Nick