Exchange Single Instance Storage (SIS)
What is SISSIS creates a single instance of messages sent to multiple recipients within the same database. Simply said, the first one gets a copy of the message in his or her mailbox, others get a referral to the message.
Why it was used?In old days where Storage were really limited, most of the mailboxes reside on a single database, and even the Disk Disk performance was not that good and the good performance disk was really expansive, so SIS saved a lot of Disk IO and space.
So what is the benefit:This Really save a lot of space and Disk IO on the database.
Exchange SIS was used on all version of Exchange from the beginning till Exchange 2007, In exchange 2007 SIS will only be enabled to the attachments only, which wont offer much regarding for performance or disk space saving.
Why its being removed?Starting the disk price are getting low and storage now are cheap.
Users mailboxes are distributed between several database.
Microsoft had enhanced ESE performance more than all other previous version of Exchange, so SIS will not be the performance saving anymore.
Microsoft ESE now compress the message Body and header by default which will be a better saving.
What about Attachments, are they compress too?The answer is NO, There is no need to compress the attachment for:
1- compressing and decompressing will be CPU intensive
2- Most of the attachments are already in compressed state (Zip - PDF - Docx - JPG)
Is compression the answer to replacing single instancing all together?The answer to that question is that it really does depend. There are certain scenarios where SIS may be viable:
Environments that only send Rich-Text Format messages. The compression algorithms in Exchange 2010 do not compress RTF message blobs because they already exist in their most compressible form.
Sending large attachments to many users. For example, sending a large (30 MB+) attachment to 20 users. Even if there were only 5 recipients out of the 20 on the same database, in Exchange 2003 that meant the 30MB attachment was stored once instead of 5 times on that database. In Exchange 2010, that attachment is stored 5 times (150 MB for that database) and isn’t compressed. But depending on your storage architecture, the capacity to handle this should be there. Also, your email retention requirements will help here, by forcing the removal of the data after a certain period of time.
Business or organizational archives that are used to maintain immutable copies of messaging data benefit from single instancing because the system only has to keep one copy of the data, which is useful when you need to maintain that data indefinitely for compliance purposes.
Community thinks?- Even if disk are cheap, we still need to take care of it insted of wasting the space for having several copy of the email !
Yes, sure but content compression should offer a good disk saving.
- And what about attachment?
Simply if you really have it as an issue, you will need use Sharepoint or third party email attachment management.
- What is the Compression MS used
- From Here
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