A Research On Distributed Image Storage For Desktop Virtualization

Due to network bandwidth limit, poor scalability and high cost, traditional NAS、SAN can only support small-scale users. The distributed storage solutions such as GFS、PVFS and other storage systems are low cost, scalability and mass storage, but only aredesigned for specific application scenarios and they can’t meet the needs of desktopvirtualization storage.Desktop virtualization image distributed storage system is designed for the I/Ocharacteristics of desktop virtualization, and it provide low cost and high scalabilitystorage. Desktop virtualization environment mainly I/O feature is small random I/O andhigh IOPS. Multiple virtual machines on the same physical machine frequent read-onlyaccess the root image. Snapshot is a very common operation, often will do a multi-levelincremental snapshot. Desktop virtualization image distributed storage system consists ofthe following four components: VMS driver, metadata servers, data servers, managementservers. VMS driver uses asynchronous blktap driver and the frequently read-only accessblocks are cached locally. VMS driver uses consistent hashing algorithm to address datawithout going through the metadata server, thus greatly reduces the pressure of metadataserver. The system is lightweight metadata server architecture, which is combined with theadvantages of centralized design and decentralized design. Metadata server only recordsthe distribution of images and the status of the data server. Image uses COW B+tree datastructure. In order to enhance the performance of random writes, first blocks are recordedin the log and then the blocks are written to memory cache. When the cache reaches acertain threshold, data is written to disk.Function tests shows that desktop virtualization image distributed storage systemprovides distributed image storage and snapshot, and provides WEB managementinterface to facilitate the use of the entire system. Performance tests show that sequentialread performance can reach60MB/S, sequential write performance can reach70MB/S.Snapshots can be achieved less than1ms. Read write performance and snapshotperformance meet the demand for desktop virtualization.