Exchange 2010 Archiving #1: No SIS

This is the first of a series of bulletins on important features of Exchange archiving, namely: single instance storage, retention management, PST management, mailbox size, multi-mailbox search, and item-level restore. Beginning with Exchange 2010, many small and medium-size organizations may find that sufficient features are included, so that third-party archiving tools are no longer necessary.

One of the lesser-known changes to Exchange 2010 is the removal of single instance storage (SIS). The reason for this is related to an architectural change, disk I/O performance, and the availability of cheap disk.

There tends to be a trade-off between better disk I/O performance and reduced storage capacity. Architecturally, Exchange 2010 introduces a new per-mailbox table structure that replaces the original per-database table structure. The original per-database table structure was optimized for SIS, but disk I/O suffered. The new per-mailbox table structure improves disk I/O, but without SIS.

In place of SIS, Exchange 2010 uses compression. Only large, redundant attachments files truly benefit from SIS; otherwise, compression delivers roughly the same volume of data as SIS.

For further information, see this Exchange team blog discussion.

... Bob Spurzem

In addition to his role as Ferris analyst, Bob is director of product marketing at Permabit, which offers a grid–based disk storage system.

One Comment

  1. Posted March 3, 2010 at 7:48 AM | Permalink

    So wouldn’t it make more sense to compress and SIS? Like most of the archiving vendors do, including us – ComArchive (

    I can’t agree that it’s better in most cases, tho. If I have an attachment which is, say, 1meg, and compresses to 100K (90%):

    If I SIS + Compress, it’s 100K
    If I SIS it, it’s 1meg
    If I compress it, it’s 100K

    But if I send it to 100 people (not exactly uncommon):

    SIS + Compress, it’s 100K
    SIS, it’s 1meg
    Compress it, it’s 10meg.

    So while for smaller numbers of recipients, it’s ok, once it gets sent to a lot of people, that breaks down pretty quickly. A big one I’ve seen is email footer images – in some companies, the same image is on the bottom of every email sent. Without SIS, thats a lot of wasted space.

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