A computer-implemented method, the method comprising: receiving a first disk access request for disk input/output (I/O) access on a virtual disk of a virtual machine, the virtual disk emulating a local physical disk for the virtual machine; wherein the virtual disk includes logical data blocks that map to physical data blocks distributed among multiple physical storage devices, deriving a simulated latency cost for the requested disk I/O access according to one or more latency and throughput characteristics of the local physical disk emulated by the virtual disk, the simulated latency cost including a simulated data transfer latency and a simulated random access latency for carrying out the requested disk I/O access on the local physical disk emulated by the virtual disk; and upon determination that the simulated latency cost of the first disk access request is at or below the current value of the disk access service quota allotted to the virtual disk: carrying out the requested disk I/O access of the first disk access request; and deducting the simulated latency cost of the requested I/O access from the current value of the disk access service quota allotted to the virtual disk; and upon determination that the simulated latency cost of the first disk access request exceeds the current value of the disk access service quota allotted to the virtual disk: queuing the first disk access request until the current value of the disk access service quota has reached at or above the simulated latency cost of the first disk access request through scheduled replenishing; wherein the current value of the disk access service quota is replenished over time, is capped at a predetermined cap value, and is decreased by a respective simulated latency cost of each previous disk access request for the virtual disk when respective requested disk I/O access of the previous disk access request was carried out; carrying out requested I/O accesses for multiple disk access requests in parallel on the multiple physical storage devices, provided that the current value of the disk access quota is above a sum of respective simulated latency costs of the multiple disk access requests; keeping a record of respective end positions of one or more previous disk access requests for the virtual disk that were received during a predetermined time interval immediately prior to a current time; and calculating the simulated random access latency for the requested disk I/O access of the first disk access request based at least on a seek distance between a start position of the requested disk I/O access and a nearest end position among the respective end positions of the one or more previous disk access requests. receiving a first disk access request for disk input/output (I/O) access on a virtual disk of a virtual machine, the virtual disk emulating a local physical disk for the virtual machine; wherein the virtual disk includes logical data blocks that map to physical data blocks distributed among multiple physical storage devices, deriving a simulated latency cost for the requested disk I/O access according to one or more latency and throughput characteristics of the local physical disk emulated by the virtual disk, the simulated latency cost including a simulated data transfer latency and a simulated random access latency for carrying out the requested disk I/O access on the local physical disk emulated by the virtual disk; and upon determination that the simulated latency cost of the first disk access request is at or below the current value of the disk access service quota allotted to the virtual disk: carrying out the requested disk I/O access of the first disk access request; and deducting the simulated latency cost of the requested I/O access from the current value of the disk access service quota allotted to the virtual disk; and carrying out the requested disk I/O access of the first disk access request; and deducting the simulated latency cost of the requested I/O access from the current value of the disk access service quota allotted to the virtual disk; and upon determination that the simulated latency cost of the first disk access request exceeds the current value of the disk access service quota allotted to the virtual disk: queuing the first disk access request until the current value of the disk access service quota has reached at or above the simulated latency cost of the first disk access request through scheduled replenishing; wherein the current value of the disk access service quota is replenished over time, is capped at a predetermined cap value, and is decreased by a respective simulated latency cost of each previous disk access request for the virtual disk when respective requested disk I/O access of the previous disk access request was carried out; carrying out requested I/O accesses for multiple disk access requests in parallel on the multiple physical storage devices, provided that the current value of the disk access quota is above a sum of respective simulated latency costs of the multiple disk access requests; keeping a record of respective end positions of one or more previous disk access requests for the virtual disk that were received during a predetermined time interval immediately prior to a current time; and calculating the simulated random access latency for the requested disk I/O access of the first disk access request based at least on a seek distance between a start position of the requested disk I/O access and a nearest end position among the respective end positions of the one or more previous disk access requests.