
FlashCopy provides a point-in-time copy
Time
Source Target
Write Read | Read |
| Write |
T0
FlashCopy command issued
Copy immediately available
Read and write to both source and copy possible
When copy is complete, relationship between source and target ends
Figure 6-1 FlashCopy concepts
When a FlashCopy operation is invoked, the process of establishing the FlashCopy pair and creating the necessary control bitmaps takes only a few seconds to complete. Thereafter, you have access to a
After creating the bitmaps, a background process begins to copy the
Read from the source volume
When you read some data from the source volume, it is simply read from the source volume.
Read from the target volume
When you read some data from the target volume, FlashCopy checks the bitmaps and:
–If the backup data is already copied to the target volume, it is read from the target volume.
–If the backup data is not copied yet, it is read from the source volume.
Write to the source volume
When you write some data to the source volume, at first the updated data is written to the data cache and persistent memory (write cache). And when the updated data is destaged to the source volume, FlashCopy checks the bitmaps and:
–If the backup data is already copied, it is simply updated on the source volume.
–If the backup data is not copied yet, first the backup data is copied to the target volume, and then it is updated on the source volume.
Write to the target volume
When you write some data to the target volume, it is written to the data cache and persistent memory, and FlashCopy manages the bitmaps to not overwrite the latest data. FlashCopy does not overwrite the latest data by the physical copy.
Chapter 6. Copy Services 91