'''Sparse file''' is a file that contains blocks of zeroes that are not allocated on disk (see [[w:Sparse file]]). By design, ploop images can't contain such non-allocated blocks.

While ploop is never creating sparse image files, they can be accidentally made so when tools such as <code>rsync --sparse</code> or <code>cp --sparse=always</code> are used to copy images. So, one should not use backup or copy tools that create sparse files out of non-sparse ones.

In case sparse file is detected by the kernel, it gives a warning in dmesg, for example:

In case there are no other ploop-related warnings or errors immediately after, this one is harmless ({{B|2825}}).

You might see something like this (reported by ploop library) during container start or mount:

Error in fill_hole (check.c:456): Warning: ploop image '/vz/private/1407/root.hdd/root.hdd' is sparse

Reallocating sparse blocks back

The last line tells that ploop library is going to fix the problem.

Since [[Download/ploop/1.10|ploop-1.10]], ploop images are checked for being sparse and are automatically fixed on mount, in case DiskDescriptor.xml is used. Otherwise, you can use <code>ploop check --repair-sparse</code> to check for and repair such images.

* [[Ploop]]

* [[w:Sparse file]]

[[Category: Storage]]

[[Category: Troubleshooting]]