Difference between revisions of "Ploop/sparse"

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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.
 
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.
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== Kernel warning ==
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In case sparse file is detected by the kernel, it gives a warning in dmesg, for example:
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Nov 21 20:37:27 sun kernel: [43451.057489] ploop(24002): a hole in image file detected (0)
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In case there are no other ploop-related warnings or errors immediately after, this one is harmless ({{B|2825}}).
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== Userspace warnings ==
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You might see something like this (reported by ploop library) during container start or mount:
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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
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Error in fill_hole (check.c:456): Warning: ploop image '/vz/private/1407/root.hdd/root.hdd' is sparse
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Reallocating sparse blocks back
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The last line tells that ploop library is going to fix the problem.
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== 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.
 
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.
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Alternatively, you can just do something like this to get rid of holes. Make sure ploop file is not used!
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cat root.hdd > root.hdd2 && mv root.hdd2 root.hdd
  
 
== See also ==
 
== See also ==
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* [[Ploop]]
 
* [[Ploop]]
 
* [[w:Sparse file]]
 
* [[w:Sparse file]]
  
[[Category: ploop]]
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[[Category: Storage]]
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[[Category: Troubleshooting]]

Latest revision as of 15:27, 10 March 2021

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 rsync --sparse or cp --sparse=always 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[edit]

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 (#2825).

Userspace warnings[edit]

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[edit]

Since 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 ploop check --repair-sparse to check for and repair such images.

Alternatively, 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[edit]