Using Solid-State Drives (SSDs) for Virtual Block Devices

In a virtualized environment, the block devices on the I/O domain can be provided to guest domains by the virtual block device (VBD). As the VBD incurs low latency and no network access is involved in accessing data, VBD has been used for storing intermediate data of data-intensive applications such as MapReduce. To accelerate the performance further, SSD can be considered as a backing device of the VBD because SSD outperforms HDD by several orders of magnitude. However, the TRIM command that plays an important role in space management of SSD has not been discussed nor handled properly in the virtualized environment. In this paper, we clarify the challenges in supporting the TRIM command in the VBD configuration and propose a novel file operation, called FTRIM (file trim). The FTRIM bridges the semantic gaps among key components of VBD and makes them to be aware of the file deletion in the guest domain. As a result, the each component of VBD can utilize the space of the deleted files, and the SSD in the I/O domain can be notified by the TRIM command. Our evaluation with a prototype shows that the proposed approach achieves up to 3.47x speed-up and sustains the improved performance in the consolidated VM environment.