CRFS introduction

CRFS is an acronym which stands for 'Coherent Remote File System'. CRFS is a network protocol that lets clients share access to a file system which is hosted on a server. Its main features include:

• general-purpose "posix" file system semantics
• cache coherency
• aggressive metadata performance
• efficient and flexible snapshots
• robust data integrity protection

The implementation hosted here includes a client module for the Linux kernel and a UNIX user space server daemon. 'crfsd', the UNIX daemon which runs in userspace, provides these features by storing data in a BTRFS file system on disk.

Status as of June, 2008

CRFS is in the initial phase of design and implementation and is proceeding towards an alpha release. It is not ready for stable use and should not be trusted to reliably store data.

CRFS is made available at this early a stage so that people can participate in the design and implementation.

The following list of features will be included in the alpha release and are immediate priorities, though perhaps not in the given order:

• upgrade to a recent BTRFS disk format
• re-establish failed TCP connections
• clients should use ranges to guide inode allocation
• crfsd should verify more on-disk btrfs metadata as it reads
• open()/unlink() should enable orphan recovery
• crfsd should evict clients that timeout and reclaim their ranges
• xattrs support should be a straight-forward operation on items
• non-4k page sizes should be supported, which means inline data cleanups
• basic client cache coherency should be supported
• basic man pages would be nice
• O_DIRECT and aio should function, even if actually copying and sync

The following list of features will not be included in the alpha release:

• clients sharing cache for reading
• snapshots
• backups
• failover
• quotas
• untrusted clients
• capability handshake
• ENOSPC
• multi-device (probably)
• shared-writable mmap coherency (maybe)

Installation instructions

Download the source and follow the instructions contained in the 'docs/developer-instructions' file

$ hg clone http://oss.oracle.com/mercurial/zab/crfs crfs
$ less crfs/docs/developer-instructions

Send a mail to crfs-devel and let us know how it goes!