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Thread: Single Instance Storage?

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  1. #1
    Join Date
    Nov 2007
    Phoenix, AZ
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    Default Single Instance Storage?

    Does Zimbra support Single Instance Storage of emails/attachments to recipients that reside within my server/domain? Is this turned on by default?



  2. #2
    Join Date
    May 2006
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    Yup, there's single-instance message storage within/per each individual mailstore server for emails & attachments. So if you had 4 mailstore boxes and the email went to 3 people on each mailstore, instead of 12 copies it just stores 4. You don't have to do anything to enable this (Imapsyncing in content however doesn't apply.)

    There's also HSM (Hierarchical Storage Management) for the Network Edition (which you have) that involves moving data to other storage locations after x amount of time.
    For instance: After 30 days messages move from your fast (and usually more expensive) SCSI disks, to a SATA array so that you can keep storage costs down.

    --Deeper explanation--

    In a standard ZCS/postfix install, if you send a message to a distribution list and all of those sers are on the same MBS server, postfix creates a single LMTP transaction to deliver them. You get one blob file with hardlinks for the different users, one copy in the redologs, ie message is written at most twice.

    When you move messages around it's still a single copy if all those users are on the same mailstore. Your not transporting the blobs around, simply the pointers to them.

    When you share a folder with a user on another mailstore the mountpoint is just accessed remotely, still one instance. Unless that user on mailstore2 drags/moves/copies an email from the share (on srv1) to one of their own folders (on srv2) - then you have a new blob.

    Zimbra doesn't use any traditional mailstore like mbox or maildir. It uses a proprietary file-per-message in a hashed-like dir hierarchy linked to a MySQL database for metadata, so it is much more efficient than either. Each message/attachment/etc is represented by a file blob. Checkout Account mailbox database structure - Zimbra :: Wiki for more info. As discussed above, we also make use of hard links for identical messages that come in at the same time/ID to multiple recipients if the accounts are on the same mailstore (aka single instance storage). I seem to remember SMTP clients who hit default_destination_recipient_limit of 50 (ie: split up delivery of larger messages into new sessions when sending), or when they get 450 error 'try again later' upon hitting the receiving servers smtp_recipient_limit/smtp_recipient_overshoot_limit (1000), end up creating a new blob (have to check if it's also a new message ID).
    Last edited by mmorse; 04-01-2009 at 09:36 PM.

  3. #3
    Join Date
    Feb 2008
    Rep Power

    Default code


    I love your product. Where is SIS implmented in the code?

    thank you kindly

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