Are there any disadvantages of `cp –sparse=always`

coreutilscpsparse-files

Is there any reason not to use use --sparse=always with every invocation to cp?

info cp says:

‘--sparse=WHEN’
     A “sparse file” contains “holes”—a sequence of zero bytes that does
     not occupy any physical disk blocks; the ‘read’ system call reads
     these as zeros.  This can both save considerable disk space and
     increase speed, since many binary files contain lots of consecutive
     zero bytes.  By default, ‘cp’ detects holes in input source files
     via a crude heuristic and makes the corresponding output file
     sparse as well.  Only regular files may be sparse.

    The WHEN value can be one of the following:

…

    ‘always’
          For each sufficiently long sequence of zero bytes in the input
          file, attempt to create a corresponding hole in the output
          file, even if the input file does not appear to be sparse.
          This is useful when the input file resides on a file system
          that does not support sparse files (for example, ‘efs’ file
          systems in SGI IRIX 5.3 and earlier), but the output file is
          on a type of file system that does support them.  Holes may be
          created only in regular files, so if the destination file is
          of some other type, ‘cp’ does not even try to make it sparse.

It also says:

[…] with the following alias, ‘cp’ will use the minimum amount of space supported by the file system.

alias cp='cp --reflink=auto --sparse=always'

Why isn't --sparse=always the default?

Best Answer

There are a few reasons why it is not default, one is backwards compatibility, performance, and last but not least, the principle of least surprise.

My understanding is that when you enable this option, there is CPU overhead which might not necessarily be acceptable, besides, backwards compatibility is also key. The cp command works reliably without, it does add a little space saving, but these days, that really is negligible, in most cases at least ...

I think the comments you received also highlighted other reasons.

Principle of least surprise means you do not change something needlessly, cp has been around for decades, changing its default behavior will upset many veterans.

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