+ +The above figure is another representation of reducing the disk image chain +using blockcommit. Data from Snap-1, Snap-2, Snap-3 are merged(/committed) +into RootBase, & now the current 'Active' image now pointing to 'RootBase' as its +backing file(instead of Snap-3, which was the case *before* blockcommit). Note +that, now intermediate images Snap-1, Snap-1, Snap-3 will be invalidated(as they were
......................................................Snap-1,Snap-2,........
+dependent on a particular state of RootBase).
+ +blockpull .................................................................... +**Figure-5** +:: + + .------------. .------------. .------------. .------------. .------------. + | | | | | | | | | | + | RootBase <--- Snap-1 <--- Snap-2 <--- Snap-3 <--- Snap-4 | + | | | | | | | | | (Active) | + '------------' '------------' '------------' '------------' '------------' + | | \ + | | \ + | | \ + | | \ stream data + | | stream data \ + | stream data | \ + | | v + .------------. | '---------------> .------------. + | | '---------------------------------> | | + | RootBase | | Snap-4 | + | | <---------------------------------------- | (Active) | + '------------' Backing File '------------' + + + +The above figure illustrates that, using block-copy we can pull data from
.......................................................using blockpull .................................
+Snap-1, Snap-2 and Snap-3 into the 'Active' layer, resulting in 'RootBase' +becoming the backing file for the 'Active' image (instead of 'Snap-3', which was +the case before doing the blockpull operation).
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+ + +Method (2) +---------- +To end up with this image chain : **base <- sn1 <- sn3** (by copying *sn2* into *sn3*) + + (a) Copy contents of sn2(the old backing file) into sn3, and change the backing file link of sn3 to sn1:: + + # qemu-img rebase -b sn1.qcow2 sn3.qcow2 + + - Apart from changing backing file link of sn3 to sn1, the above cmd + will it also /copy/ the contents from sn2 into sn3). + + - In other words: This is 'Safe mode', which is the default -- + any clusters that differ between the new backing_file(in this + case, sn1) and the old backing file(in this case, sn2) of + filename(in this case, sn3) are merged into filename(sn3), before + actually changing the backing file. + + (b) Now, we can delete the sn2 disk image(as the changes are now committed to + sn1). ::
...........................................................(as the changes are now merged into sn3).......
+ + # rm sn2.qcow2 +
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