Editing Ploop/sparse

'''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.

== Kernel warning ==

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

 Nov 21 20:37:27 sun kernel: [43451.057489] ploop(24002): a hole in image file detected (0)

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

== Userspace warnings ==

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

 Error in check_and_repair_sparse (check.c:542): Delta file /vz/private/1407/root.hdd/root.hdd contains uninitialized blocks (offset=135573536768 len=1323008) which are not aligned to cluster size
 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.

== How to fix ==

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.

Alternatelely, you can just do something like this to get rid of holes. Make sure ploop file is not used!

 cat root.hdd > root.hdd2 && mv root.hdd2 root.hdd

== See also ==

* [[Ploop]]
* [[w:Sparse file]]

[[Category: Storage]]
[[Category: Troubleshooting]]