Most of user asked me what are basic differences between EMC Clone/Mirror/Snapshot? This is really confusing terminology because most of things will be same logically.Only thing change that is implementation and purpose of uses. I am trying to write basic and common differences:

1) A clone is a full copy of data in a source LUN. A snapshot is a point-in time "virtual" copy that does not occupy any disk space.
2) A snapshot can be created or destroyed in seconds, unlike a clone or mirror. A clone, for example, can take minutes to hours to create depending on the size of the source LUN.
3) A clone or mirror requires exactly the same amount of disk space as the source LUN. A snapshot cache LUN generally requires approximately 10% to 20% of the source LUN size.
4) A clone is an excellent on-array solution that enables you to recover from a data corruption issue. Mirrors are designed for off-site data recovery.
5) A clone is typically fractured after it is synchronized while a mirror is not fractured but instead is actively and continuously being synchronized to any changes on the source LUN
Clones and mirrors are inaccessible to the host until they are fractured. Clones can be easily resynchronized in either direction. This capability is not easily implemented with mirrors.
Restoring data after a source LUN failure is instantaneous using clones after a reverse synchronization is initialized. Restore time from a snapshot depends on the time it takes to restore from the network or from a backup tape.
Once a clone is fractured, there is no performance impact (that is, performance is comparable to the performance experienced with a conventional LUN). For snapshots, the performance impact is above average and constant due to copy on first write (COFW).

I left one more term EMC BCV(Business Continuity Volume). It is totally different concept thought. I will try to cover in upcoming post though I have discussed about EMC BCV in my older post. But it is more or less cloning only only implementation change.


  1. Anonymous Says:
  2. First of all.. Just wanted to say that this blog is "JUST AWESOME".

    Could you please emphasize on the differences between a TF-Clone and TF-BCV?

  3. Anonymous Says:
  4. One key difference is that a BCV/mirror occupies a mirror postion ( maximum of 4 )while a clone doesn't.

  5. Anonymous Says:
  6. True I get some of the advantages of clone over BCV- Mirror postion independence, Resynchronization flexibility,clones when activated can be accessed even while established etc.. then when would we prefer a BCV/mirror over a Clone?

  7. Anonymous Says:
  8. Please define the basic Architecture of the clariion CX-3 series?

  9. Anonymous Says:
  10. One of the best simple documentation........... :)-

  11. Anonymous Says:
  12. yea..gud/simple documentation...:-)

  13. Anonymous Says:
  14. Qu:- One key difference is that a BCV/mirror occupies a mirror postion ( maximum of 4 )while a clone doesn't.

    Ans:-RAID1 & RAID5 M2,And With SRDF M3,BCV M4

  15. Anonymous Says:
  16. You put the technology in simple words, Thanks

  17. Anonymous Says:
  18. Excellent blog with wonderful information. Thank you Diwakar!

    Some commands that need to be remembered:

    symclone (usually clones, from SRDF-ed source devices) and symmir (BCVs).

    Primary difference while using these:
    - symmir need to have devices with BCV attribute to create a mirror copy.
    - symclone can be done on any standard device (no need to have a device with BCV attribute).

  19. Anonymous Says:
  20. Awesome blog..

    can you please clarify the below query
    Does snapshot holds any mirror position in symmetrix?

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