cockroach debug ballast

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As of May 10, 2022, CockroachDB v20.2 is no longer supported. For more details, refer to the Release Support Policy.

The cockroach debug ballast command creates a large, unused file that you can place in a node's storage directory. In the case that a node runs out of disk space and shuts down, you can delete the ballast file to free up enough space to be able to restart the node.

  • Do not run cockroach debug ballast with a unix root user. Doing so brings the risk of mistakenly affecting system directories or files.
  • Do not name the target file similar to a block device in /dev. Doing so brings the risk of mistyping a /dev prefix into the command and thereby corrupting a filesystem.
  • In addition to placing a ballast file in each node's storage directory, it is important to actively monitor remaining disk space.
  • Ballast files may be created in many ways, including the standard dd command. cockroach debug ballast uses the fallocate system call when available, so it will be faster than dd.


While the cockroach debug command has a few subcommands, users are expected to use only the zip, encryption-active-key, merge-logs, and ballast subcommands.

The other debug subcommands are useful only to CockroachDB's developers and contributors.


Create a ballast file:

$ cockroach debug ballast [path to ballast file] [flags]

View help:

$ cockroach debug ballast --help


Flag Description
The amount of space to fill, or to leave available, in a node's storage directory via a ballast file. Positive values equal the size of the ballast file. Negative values equal the amount of space to leave after creating the ballast file. This can be a percentage (notated as a decimal or with %) or any bytes-based unit, for example:

--size=1000000000 ----> 1000000000 bytes
--size=1GiB ----> 1073741824 bytes
--size=5% ----> 5% of available space
--size=0.05 ----> 5% of available space
--size=.05 ----> 5% of available space

Default: 1GB


Create a 1GB ballast file (default)

$ cockroach debug ballast cockroach-data/ballast.txt

Create a ballast file of a different size

$ cockroach debug ballast cockroach-data/ballast.txt --size=2GB

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