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→Write tracker: more info
Write tracker is a feature of ploop that aims during live migration. When write tracker is turned on, kernel memorizes a list of modified data blocks. This list then can be used to efficiently migrate a ploop device to a different physical server, with minimal container downtime. User-space support for this is implemented in '''ploop copy''' tool and is used by '''vzmigrate''' utility.
The idea is to do iterative migration of an image file, in the following
way:
# Turn write tracker feature on. Now the kernel will keep track of ploop image blocks being modified.
# Copy all blocks of a ploop image file to a destination system.
# Ask write tracker which blocks were modified.
# Copy only these blocks.
# Repeat steps 3 and 4 until number of blocks is not decreasing.
# Freeze the container processes and repeat steps 3 and 4 last time.
See [http://openvz.livejournal.com/41835.html Effective live migration with ploop write tracker] blog post for more details.
== Benefits ==
