Disk Environment Overv iew 87
• Only one set of write operations to disk in continuous physical sequence
(insteadof a set of random writes), which is the most optimized write mode for
RAID technology
Figure 23 on page 87 and Figure 24 on page 87 illustrate the LSF concept.
Figure 23. LSFConcept 1
The main challenge ofan LSF architecture is managing the free space. Because
the LSF log has to be never-ending,an LSF system must always have enough
free space for writingnew data. Over time, old copies of data begin to fragment
the log, so to reclaim free space, some type of automatic cleaning routine must
be hardware implemented to defragment the log. This cleaning is often referred
to as garbage or free space collection. Thebenef itsof LSF outweigh the
overhead offree space collection.
Figure 24. LSFConcept 2
The timed view of a volume, throughan i nstantaneous duplicationof the table
representation of avolume, allows two independent views of the same physical
data without anydat a moveprocess. So each view can do independent updates
that are separatelyrecorded, while the common unchanged part is still shared.
Figure 25 on page 88 shows an overview of snapping a volume with SnapShot.
Log Structured File
SHIP'S LOG49D12.26N 123D14.92W
49D14.07N 123D16.04W
49D19.69N 123D16.22W
Onlythe last position isvalid!
Log Structured File...
LOG
DATA
DATA
DATA
DATA
DATA
DATA
DATA
DATA