[SOLVED] dd to sparse file?

qrange · 06-27-2018, 07:09 AM

I'd like to copy a part of normal fileA to a (already) sparse fileB :

Code:

dd if="fileA" of="fileB" bs=2k count=3 skip=2 seek=2

however, fileB looses its 'sparsity'. is there a way to do it?
thanks.

edit:
nevermind, I probably should have used 'oflag=append conv=notrunc'
anyway, ignore.

pan64 · 06-27-2018, 08:02 AM

that will append to the [sparse] fileB, regardless of its original size and content. You cannot write into it this way. To write into that "sparse" area is another thing.

rknichols · 06-27-2018, 09:36 AM

Include the "conv=sparse" option. That will cause dd to just seek over any all-zero blocks rather than copying the zeros, though I'm not sure what happens if fileA has an all-zero block at an offset where fileB has existing non-zero data. A literal reading of the dd manpage suggests that the non-zero data in fileB would remain. (I'm not quite motivated enough to test that.)

And BTW, you'll also need the "conv=notrunc" option if you want to preserve any existing part of fileB.