A computer-implemented method executed by one or more processors for measuring performance metrics in a distributed storage system, the method comprising: identifying requests sent by clients to the distributed storage system, each request including request parameter values for request parameters including a request target; generating probe requests based on the identified requests, the probe requests including probe request parameter values for probe request parameter values, representing a statistical sample of the request parameters included in the identified requests; sending the generated probe requests to the distributed storage system over a network with an indication that the probe requests are not sent by a client, wherein the distributed storage system is configured to: in response to receiving the probe requests, perform preparations for servicing each probe request that would also be performed for servicing a corresponding request that is received from a client, and based on the indications that the probe requests are not sent by a client, instead of accessing data indicated by the request target, accessing data specifically allocated for a prober; receiving responses to the probe requests from the distributed storage system; and outputting at least one performance metric value measuring a current performance state of the distributed storage system based on the received responses; wherein the request parameters include a request type, concurrency parameters, and a request target indicating data within the distributed storage system to which the request pertains, and wherein generating the probe requests includes generating a number of probe requests including a particular request type, particular concurrency parameters, and a particular request target that is proportional to a number of identified requests including the particular request type, the particular concurrency parameters, and the particular request target. identifying requests sent by clients to the distributed storage system, each request including request parameter values for request parameters including a request target; generating probe requests based on the identified requests, the probe requests including probe request parameter values for probe request parameter values, representing a statistical sample of the request parameters included in the identified requests; sending the generated probe requests to the distributed storage system over a network with an indication that the probe requests are not sent by a client, wherein the distributed storage system is configured to: in response to receiving the probe requests, perform preparations for servicing each probe request that would also be performed for servicing a corresponding request that is received from a client, and based on the indications that the probe requests are not sent by a client, instead of accessing data indicated by the request target, accessing data specifically allocated for a prober; in response to receiving the probe requests, perform preparations for servicing each probe request that would also be performed for servicing a corresponding request that is received from a client, and based on the indications that the probe requests are not sent by a client, instead of accessing data indicated by the request target, accessing data specifically allocated for a prober; receiving responses to the probe requests from the distributed storage system; and outputting at least one performance metric value measuring a current performance state of the distributed storage system based on the received responses; wherein the request parameters include a request type, concurrency parameters, and a request target indicating data within the distributed storage system to which the request pertains, and wherein generating the probe requests includes generating a number of probe requests including a particular request type, particular concurrency parameters, and a particular request target that is proportional to a number of identified requests including the particular request type, the particular concurrency parameters, and the particular request target.