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symsnap question
Hi,
Am trying to understand the concepts. Please help me on this.
1. After snap is created, If I update data on target (DEV) device, where does this change go to? Is it source device or save device pool?
2. After snap is created, If I update data on source device, where does this change go to? Is it source or save device pool?
Thanks.
Quincy561
1.3K Posts
1
September 2nd, 2010 12:00
Just to be clear on the terms, when you create a snap, it is not yet active, so it is not ready to the host. It has to be activated which creates the point in time copy.
When it is activated, the 1st write to a given track on the source will push that track to the SAV pool. Any further writes to that same track won't copy anything anywhere.
All writes to the snap copy will go to the SAV pool, partial track writes will need to be merged with the original data on the source.
Booyah2
184 Posts
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September 14th, 2010 13:00
Hello Kaizen10,
I have attached the Product Guide for your reference, I hope this helps with your understanding the product...it does get confusing.
Also, There is a EMC Business Continuity Management Class that you could sign up for and SNAP is discussed in depth.
This is a brief description from the course manual.
Module 3 - TimeFinder/Snap Operations - 5
© 2009 EMC Corporation. All rights reserved. Module 3 - TimeFinder/Snap Operations - 5
Once the TimeFinder/Snap session is activated
–
The first time a track on the source is written to, the original data on the
source is copied to the save device, the VDEV pointer is changed to point
to the save device; “then” the source is changed.
–
“Copy on First Write” applies to writes to the VDEV as well.
TimeFinder/Snap uses a process called “Copy on First Write” when a Snap session is activated. When a host attempts to write to a track on the Source volume for the first time after activation, the original track is copied from the Source volume to the Save Area, the pointer is updated to reference the Save Area, then the Source volume is updated with the new write. Subsequent writes to the same track on the Source volume will not invoke a data copy. Likewise, when a write is issued to a track on the VDEV for the first time, the original data is copied from the Source volume to the Save Area, the
pointer is updated, and the new write to the VDEV is stored in the Save Area.
1 Attachment
SNAP_300-007-864.pdf