If you fracture a clone in a Consistent state, the source may be receiving writes from the host that have not been copied to the clone. If you want the clone to be a byte-for-byte copy of the source, you must ensure that no host writes are occurring when you fracture the clone.
By waiting until the clone is in a Synchronized state, you can have some confidence that host writes are no longer occurring. The Synchronized state indicates that some number of seconds, which is set by the quiesce threshold property, have elapsed since the last host write. However, it does not guarantee that another host write will not occur around the same time you fracture the clone.
If the clone never enters the Synchronized state, host writes are still continuing. However, it may be difficult to determine the reason for those writes. For example, they can be due to heartbeats in some clustered systems.
In some cases it is useful to fracture the clone in a Consistent state. For instance, you would fracture a clone in a Consistent state when
you can determine that I/O is no longer being issued to the source LUN and prefer not to wait for the quiesce threshold to elapse.
you only need a crash consistent image (the image you would have if the host crashed).
your application has a hot backup mode in which the application continues to write to the source, but internally understands how to ignore writes generated after your specified point-in-time.
Parks2
116 Posts
571
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Posted September 15th, 2010 04:00
EMC Primus emc96986
If you fracture a clone in a Consistent state, the source may be receiving writes from the host that have not been copied to the clone. If you want the clone to be a byte-for-byte copy of the source, you must ensure that no host writes are occurring when you fracture the clone.
By waiting until the clone is in a Synchronized state, you can have some confidence that host writes are no longer occurring. The Synchronized state indicates that some number of seconds, which is set by the quiesce threshold property, have elapsed since the last host write. However, it does not guarantee that another host write will not occur around the same time you fracture the clone.
If the clone never enters the Synchronized state, host writes are still continuing. However, it may be difficult to determine the reason for those writes. For example, they can be due to heartbeats in some clustered systems.
In some cases it is useful to fracture the clone in a Consistent state. For instance, you would fracture a clone in a Consistent state when