Changes

Everything you wanted to know about DISKINODES for ploop but were afraid to ask.

With simfs layout, vzquota is used to set limits for DISKSPACE and

DISKINODES, so these limits can be changed any time.

Unlike simfs, ploop contains a real file system, so amount of disk space

and disk inodes are properties of the file system, determined while

inodes.

{{Note|There is no way to change DISKINODES for existing ploop. This is a limitation of ext4.}}

In other words, <code>vzctl set --diskinodes</code> is ignored for ploop layout -- it can only be specified on create.

By default, ext4 allocates 1 (one) inode per each 16 KB of data; this is

practically the same as to assume that the average file size will be 16KB.

For example, when creating a ploop with 40GB of disk space, 2621440 inodes

will be available:

<math>\frac{40 * 1024 * 1024}{16} = 2621440</math>

If the above default is too low for your usage (for example, a container

has or will have too many small files), you can specify a larger value

for DISKINODES '''during container creation or conversion only'''.

{{Note|The feature works since vzctl 4.7.}}

{{Note|You can only specify <code>--diskinodes</code> for <code>vzctl create</code> or <code>vzctl convert</code>.}}

The way it works is the following. First, a file system big enough

to accommodate the requested number of DISKINODES is created, and then

requested amount of DISKSPACE.

Example:

Here, a filesystem big enough to have 5242880 of diskinodes

will be created (it's 5242880 * 16K = 80G), then downsized to 40G.

Sometimes, when the amount of DISKINODES specified is too high,

a very large filesystem is created, and it can not be downsized

shown when converting a container from simfs to ploop:

...

vzctl convert ''CTID''

Failed to resize image: Error in ploop_resize_image (ploop.c:2477): Unable to change image size to 83877888 sectors, minimal size is 502423144 [38]

In this case, 1G inodes requirement leads to creation of 16TB filesystem

(remember, 1 inode per 16K). Unfortunately, such huge FS can't be downsized

the error message are in sectors which are 512 bytes each).

'''Solution 1''': please be reasonable when requesting diskinodes for ploop.

'''Solution 2''': please set DISKINODES to 0 before conversion:

vzctl set ''CTID'' --diskspace ''xxx''G --diskinodes 0 --save

vzctl convert ''CTID''

This will lead to creating a filesystem with default number of inodes.

If DISKINODES specified during <code>create</code> or <code>convert</code> is

lower than the default (1 inode per 16K of disk space), it is silently ignored.

In other words, there is no way to limit DISKINODES to lower than DISKSPACE / 16384.

* {{git commit|vzctl|ef320d32a4}}

* https://lists.openvz.org/pipermail/users/2014-October/005913.html

[[Category: Storage]]