Optimize I/O

Redpanda relies on its own disk I/O scheduler, and by default, it tells the kernel to use the noop scheduler. Additionally, rpk comes with an embedded database of I/O settings, which are specific combinations of CPUs, SSD types, and VM sizes. Because running software on four VCPUs isn’t the same as running on an EC2 i3.metal with 96 physical cores, Redpanda tries to predict the best known settings for VM cloud types.

rpk iotune is a tool to optimize I/O performance for a specific Redpanda instance and its hardware. It runs benchmarks to capture the read/write IOPS and bandwidth capabilities of a node, then it outputs parameters to an I/O configuration file (io-config.yaml) that Redpanda reads upon startup to optimize itself for the node. rpk iotune by default saves its I/O configuration file to /etc/redpanda/io-config.yaml, and Redpanda by default reads from there at startup.

It isn’t necessary to run rpk iotune each time Redpanda is started, as its I/O output configuration file can be reused in nodes running on the same type of hardware. Reuse an I/O output configuration file by starting Redpanda with the --io-properties-file flag and the path to the file:

Alternatively, the contents of the I/O configuration file can be converted to a string, and the string can be passed with the --io-properties flag:

Currently in its database of I/O settings, Redpanda has well-known-types for AWS and GCP. On startup, rpk tries to detect the cloud and instance type from the cloud’s metadata API, setting the correct iotune properties.

If access to the metadata API isn’t allowed from the instance, you can hint the desired setup by passing the --well-known-io flag with the cloud vendor, VM type, and storage type:

It can also be specified in the redpanda.yaml configuration file, under the rpk object:

If a certain cloud vendor, machine type, or storage type isn’t found, or if the metadata isn’t available and no hint is given, then rpk prints a warning and continues to use the default values.