# RBD Replay¶

RBD Replay is a set of tools for capturing and replaying RADOS Block Device (RBD) workloads. To capture an RBD workload, lttng-tools must be installed on the client, and librbd on the client must be the v0.87 (Giant) release or later. To replay an RBD workload, librbd on the client must be the Giant release or later.

Capture and replay takes three steps:

1. Capture the trace. Make sure to capture pthread_id context:

mkdir -p traces
lttng create -o traces librbd
lttng enable-event -u 'librbd:*'
lttng start
lttng stop

2. Process the trace with rbd-replay-prep:

rbd-replay-prep traces/ust/uid/*/* replay.bin

3. Replay the trace with rbd-replay. Use read-only until you know it’s doing what you want:

rbd-replay --read-only replay.bin


Important

rbd-replay will destroy data by default. Do not use against an image you wish to keep, unless you use the --read-only option.

The replayed workload does not have to be against the same RBD image or even the same cluster as the captured workload. To account for differences, you may need to use the --pool and --map-image options of rbd-replay.