Patrick Donnelly

Ceph was originally designed to fill a need for a distributed file system within scientific computing environments but has since grown to become a dominant unified software-defined distribute storage system. Today, it is also notably used as an enterprise-quality block device and object store provider. This talk will cover the new development of an SQLite Virtual File System (VFS) on top of Ceph's distributed object store (RADOS). I will show how SQL can now be run on Ceph for both its internal use and for new application storage requirements.

The talk will cover:

• Existing storage abstractions on Ceph.
• Very brief introduction to RADOS.
• Very brief introduction to SQLite and its VFS abstraction.
• The libcephsqlite library and how it works.
• How to use libcephsqlite in an application.
• How Ceph uses libcephsqlite.
• What's in the future?

Metadata-heavy workloads are often the bane of networked and clustered filesystems. Directory operations (create and unlink, in particular) usually involve making a synchronous request to a server on the network, which can be very slow.

CephFS however has a novel mechanism for delegating the ability for clients to do certain operations locally. While that mechanism has mostly been used to delegate capabilities on normal files in the past, it's possible to extend this to cover certain types of directory operations as well.

The talk will describe work that is being done to bring asynchronous directory operations to CephFS. It will cover the design and tradeoffs necessary to allow for asynchronous directory operations, discuss the server and client-side infrastructure being added to support it, and what performance gains we expect to gain from this.

• overview of problem (why metadata operations are so slow on network filesystems) and proposed solution
• CephFS caps
• DIRUNLINK and DIRCREATE caps
• directory completeness and dentry revalidation
• asynchronous unlink
• Inode number delegation
• asynchronous creates
• benchmarks
• what about error handling?