Monday, October 27, 2008

XtreemFS 0.10.0 released: checksums and more

We have just released XtreemFS 0.10.0 on Apart from many quality improvements, it contains several exciting new features:
  • checksum support for file objects, including xtfs_scrub for verification
  • client: caching, improved performance, new platforms (win32, ARM, OS X)
  • UUIDs
  • OSD cleanup
  • plug-in interface
Made popular by ZFS, checksums allow you to verify the integrity of your file data. XtreemFS OSD can now compute, maintain and verify checksums for each file object. Our new scrubbing tool xtfs_scrub allows you to verify checksums on all OSDs in parallel.

Our client, an integral part of the XtreemFS architecture, is now much faster than previous versions, and you should be network or disk bound in most cases. We also added caching for file data and metadata, which also improves performance considerably. The client is now also running on Linux on ARM devices and we have added experimental ports for Windows and OS X.

XtreemFS now identifies all its services by UUIDs. This allows you to move services and their data to different hosts and use NATed network setups where only some of the IP addresses can be used.

Further, we have now a tool xtfs_cleanup for reclaiming storage space by erasing orphaned objects from OSDs (objects can be orphaned if the client crashes while deleting a file). We extend our plug-in interface in the MRC so that you can add your own policies (written in Java) to control its operation.

Friday, October 24, 2008

Client News: Caching, Win32, OS X, ARM

The client of XtreemFS contains a considerable part of the logic of XtreemFS as it has to coordinate the metadata and object storage servers (OSDs) to provide the user with a POSIX-compliant file system abstraction. 

This setup is great from an architectural view point because it scales well as it takes tasks away from the metadata and storage servers. But it also makes the client a complex beast. 

In the last weeks we have put a lot of work in the client and you will be able to use the features soon as part of the 0.10.0 release

The first area of work was caching. While the operating system already caches file data in the page cache, the granularity of the accesses are mostly 4k - too small if you have to fetch each of these over the network. With client-side caching, we can now fetch data with object granularity, which is usually a few hundred k or more. We will follow-up with real measurements soon, but the performance improvements are very good. 

Client-side caching is also laying the foundation for prefetching, RAID, and other things that are on our long-term roadmap. 

We have also implemented a metadata cache that allows the client to retrieve the results of a readdir() together with all the stat()s in one RPC - important for long-latency networks like DSL or installations over the Internet. But it also feels more snappy on the LAN.

We have also started porting the client to other platforms than Linux/FUSE. We have been running on OS X with Mac FUSE for quite a while now (available on our download page), and have now extended our coverage of platforms to Windows and ARM Linux. The Windows client is using the fantastic Dokan library with the fuse4win adapter. It will be available on the download page soon.