Zach Brown
32e7978a6e
The grace period is intended to let lock holders squeeze in more bulk work before another node pulls the lock out from under them. The length of the delay is a balance between getting more work done per lock hold and adding latency to ping-ponging workloads. The current grace period was too short. To do work in the conflicting case you often have to read the result that the other mount wrote as you invalidated their lock. The test was written in the LSM world where we'd effectively read a single level 0 1MB segment. In the btree world we're checking bloom blocks and reading the other mount's btree. It has more dependent read latency. So we turn up the grace period to let conflicting readers squeeze in more work before pulling the lock out from under them. This value was chosen to make lock-conflicting-batch-commit pass in guests sharing nvme metadata devices in debugging kernels. Signed-off-by: Zach Brown <zab@versity.com>
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
- Commit logs 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. Since the format hash-checking has now been removed in preparation for release, if there is any doubt, mkfs is strongly recommended.
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 scoutfs-devel@scoutfs.org 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:
- One or more nodes running x86-64 CentOS/RHEL 7.4 (or 7.3)
- Access to two shared block devices
- IPv4 connectivity between the nodes
The steps for getting scoutfs mounted and operational are:
- Get the kernel module running on the nodes
- Make a new filesystem on the devices with the userspace utilities
- Mount the devices on all the nodes
In this example we run all of these commands on three nodes. The names of the block devices are the same on all the nodes.
-
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 git@github.com:versity/scoutfs.git make -C scoutfs modprobe libcrc32c insmod scoutfs/kmod/src/scoutfs.ko alias scoutfs=$PWD/scoutfs/utils/src/scoutfs -
Make a New Filesystem (destroys contents, no questions asked)
We specify that two of our three nodes must be present to form a quorum for the system to function.
scoutfs mkfs -Q 2 /dev/meta_dev /dev/data_dev -
Mount the Filesystem
Each mounting node provides its local IP address on which it will run an internal server for the other mounts if it is elected the leader by the quorum.
mkdir /mnt/scoutfs mount -t scoutfs -o server_addr=$NODE_ADDR,metadev_path=/dev/meta_dev /dev/data_dev /mnt/scoutfs -
For Kicks, Observe the Metadata Change Index
The
meta_seqindex 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