7e935898ab
server_get_log_trees() sets the low flag in a mount's meta_avail allocator, triggering enospc for any space consuming allocatins in the mount, if the server's global meta_vail pool falls below the reserved block count. Before each server transaction opens we swap the global meta_avail and meta_freed allocators to ensure that the transaction has at least the reserved count of blocks available. This creates a risk of premature enospc as the global meta_avail pool drains and swaps to the larger meta_freed. The pool can be close to the reserved count, perhaps at it exactly. _get_log_trees can fill the client's mount, even a little, and drop the global meta_avail total under the reserved count, triggering enospc, even though meta_Freed could have had quite a lot of blocks. The fix is to ensure that the global meta_avail has 2x the reserved count and swapping if it falls under that. This ensures that a server transaction can consume an entire reserved count and still have enough to avoid triggering enospc. This fixes a scattering of rare premature enospc returns that were hitting during tests. It was rare for meta_avail to fall just at the reserved count and for get_log_trees to have to refill the client allocator, but it happened. 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 use three nodes. The names of the block devices are the same on all the nodes. Two of the nodes will be quorum members. A majority of quorum members must be mounted to elect a leader to run a server that all the mounts connect to. It should be noted that two quorum members results in a majority of one, each member itself, so split brain elections are possible but so unlikely that it's fine for a demonstration.
-
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=$PWD/scoutfs/utils/src/scoutfs -
Make a New Filesystem (destroys contents)
We specify quorum slots with the addresses of each of the quorum member nodes, the metadata device, and the data device.
scoutfs mkfs -Q 0,$NODE0_ADDR,12345 -Q 1,$NODE1_ADDR,12345 /dev/meta_dev /dev/data_dev -
Mount the Filesystem
First, mount each of the quorum nodes so that they can elect and start a server for the remaining node to connect to. The slot numbers were specified with the leading "0,..." and "1,..." in the mkfs options above.
mount -t scoutfs -o quorum_slot_nr=$SLOT_NR,metadev_path=/dev/meta_dev /dev/data_dev /mnt/scoutfsThen mount the remaining node which can now connect to the running server.
mount -t scoutfs -o 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