Introduction

scoutfs is a clustered in-kernel Linux filesystem designed and built from the ground up to support large archival systems.

Its key differentiating features are:

• Integrated consistent indexing accelerates archival maintenance operations
• Log-structured commits allow nodes to write concurrently without contention

It meets best of breed expectations:

• Fully consistent POSIX semantics between nodes
• Rich metadata to ensure the integrity of metadata references
• Atomic transactions to maintain consistent persistent structures
• First class kernel implementation for high performance and low latency
• Open GPLv2 implementation

Learn more in the white paper.

Current Status

Alpha Open Source Development

scoutfs is under heavy active development. We're developing it in the open to give the community an opportunity to affect the design and implementation.

The core architectural design elements are in place. Much surrounding functionality hasn't been implemented. It's appropriate for early adopters and interested developers, not for production use.

In that vein, expect significant incompatible changes to both the format of network messages and persistent structures. To avoid mistakes the implementation currently calculates a hash of the format and ioctl header files in the source tree. The kernel module will refuse to mount a volume created by userspace utilities with a mismatched hash, and it will refuse to connect to a remote node with a mismatched hash. This means having to unmount, mkfs, and remount everything across many functional changes. Once the format is nailed down we'll wire up forward and back compat machinery and remove this temporary safety measure.

The current kernel module is developed against the RHEL/CentOS 7.x kernel to minimize the friction of developing and testing with partners' existing infrastructure. Once we're happy with the design we'll shift development to the upstream kernel while maintaining distro compatibility branches.

Community Mailing List

Please join us on the open [email protected] mailing list hosted on Google Groups for all discussion of scoutfs.

Quick Start

This following a very rough example of the procedure to get up and running, experience will be needed to fill in the gaps. We're happy to help on the mailing list.

The requirements for running scoutfs on a small cluster are:

1. One or more nodes running x86-64 CentOS/RHEL 7.4 (or 7.3)
2. Access to a single shared block device
3. IPv4 connectivity between the nodes

The steps for getting scoutfs mounted and operational are:

1. Get the kernel module running on the nodes
2. Make a new filesystem on the device with the userspace utilities
3. Mount the device on all the nodes

In this example we run all of these commands on three nodes. The block device name is the same on all the nodes.

1. Get the Kernel Module and Userspace Binaries

   • Either use snapshot RPMs built from git by Versity:

   rpm -i https://scoutfs.s3-us-west-2.amazonaws.com/scoutfs-repo-0.0.1-1.el7_4.noarch.rpm
   yum install scoutfs-utils kmod-scoutfs

   • Or use the binaries built from checked out git repositories:

   yum install kernel-devel
   git clone [email protected]:versity/scoutfs-kmod-dev.git
   make -C scoutfs-kmod-dev module 
   modprobe libcrc32c
   insmod scoutfs-kmod-dev/src/scoutfs.ko
   
   git clone [email protected]:versity/scoutfs-utils-dev.git
   make -C scoutfs-utils-dev
   alias scoutfs=$PWD/scoutfs-utils-dev/src/scoutfs

2. Make a New Filesystem (destroys contents, no questions asked)

   We specify that two of our three nodes must be present to form a quorum for the system to function.

   scoutfs mkfs -Q 2 /dev/shared_block_device

3. Mount the Filesystem

   Each mounting node provides its local IP address on which it will run an internal server for the other mounts if it is elected the leader by the quorum.

   mkdir /mnt/scoutfs
   mount -t scoutfs -o server_addr=$NODE_ADDR /dev/shared_block_device /mnt/scoutfs

4. For Kicks, Observe the Metadata Change Index

   The meta_seq index tracks the inodes that are changed in each transaction.

   scoutfs walk-inodes meta_seq 0 -1 /mnt/scoutfs
   touch /mnt/scoutfs/one; sync
   scoutfs walk-inodes meta_seq 0 -1 /mnt/scoutfs
   touch /mnt/scoutfs/two; sync
   scoutfs walk-inodes meta_seq 0 -1 /mnt/scoutfs
   touch /mnt/scoutfs/one; sync
   scoutfs walk-inodes meta_seq 0 -1 /mnt/scoutfs