GekkoFS

GekkoFS is a file system capable of aggregating the local I/O capacity and performance of each compute node in a HPC cluster to produce a high-performance storage space that can be accessed in a distributed manner. This storage space allows HPC applications and simulations to run in isolation from each other with regards to I/O, which reduces interferences and improves performance.

Dependencies

• >gcc-8 (including g++) for C++11 support
• General build tools: Git, Curl, CMake >3.6 (>3.11 for GekkoFS testing), Autoconf, Automake
• Miscellaneous: Libtool, Libconfig

Debian/Ubuntu

GekkoFS base dependencies: apt install git curl cmake autoconf automake libtool libconfig-dev

GekkoFS testing support: apt install python3-dev python3 python3-venv

With testing

CentOS/Red Hat

GekkoFS base dependencies: yum install gcc-c++ git curl cmake autoconf automake libtool libconfig

GekkoFS testing support: python38-devel (>Python-3.6 required)

Step-by-step installation

1. Make sure the above listed dependencies are available on your machine
2. Clone GekkoFS: git clone --recurse-submodules https://storage.bsc.es/gitlab/hpc/gekkofs.git
   • (Optional) (Optional) If you checked out the sources using git without the --recursive option, you need to execute the following command from the root of the source directory: git submodule update --init
3. Set up the necessary environment variables where the compiled direct GekkoFS dependencies will be installed at (we assume the path /home/foo/gekkofs_deps/install in the following)
   • export LD_LIBRARY_PATH=${LD_LIBRARY_PATH}:/home/foo/gekkofs_deps/install/lib:/home/foo/gekkofs_deps/install/lib64
4. Download and compile the direct dependencies, e.g.,
   • Download example: gekkofs/scripts/dl_dep.sh /home/foo/gekkofs_deps/git
   • Compilation example: gekkofs/scripts/compile_dep.sh /home/foo/gekkofs_deps/git /home/foo/gekkofs_deps/install
   • Consult -h for additional arguments for each script
5. Compile GekkoFS and run optional tests
   • Create build directory: mkdir gekkofs/build && cd gekkofs/build
   • Configure GekkoFS: cmake -DCMAKE_BUILD_TYPE=Release -DCMAKE_PREFIX_PATH=/home/foo/gekkofs_deps/install ..
     • add -DCMAKE_INSTALL_PREFIX=<install_path> where the GekkoFS client library and server executable should be available
     • add -DGKFS_BUILD_TESTS=ON if tests should be build
   • Build and install GekkoFS: make -j8 install
   • Run tests: make test

GekkoFS is now available at:

• GekkoFS daemon (server): <install_path>/bin/gkfs_daemon
• GekkoFS client interception library: <install_path>/lib64/libgkfs_intercept.so

Run GekkoFS

General

On each node a daemon (gkfs_daemon binary) has to be started. Other tools can be used to execute the binary on many nodes, e.g., srun, mpiexec/mpirun, pdsh, or pssh.

You need to decide what Mercury NA plugin you want to use for network communication. ofi+sockets is the default. The -P argument is used for setting another RPC protocol. See below.

• ofi+sockets for using the libfabric plugin with TCP (stable)
• ofi+tcp for using the libfabric plugin with TCP (slower than sockets)
• ofi+verbs for using the libfabric plugin with Infiniband verbs (reasonably stable) and requires the rdma-core (formerly libibverbs) library
• ofi+psm2 for using the libfabric plugin with Intel Omni-Path (unstable) and requires the opa-psm2 library

The GekkoFS hostsfile

Each GekkoFS daemon needs to register itself in a shared file (hostsfile) which needs to be accessible to all GekkoFS clients and daemons. Therefore, the hostsfile describes a file system and which node is part of that specific GekkoFS file system instance. In a typical cluster environment this hostsfile should be placed within a POSIX-compliant parallel file system, such as GPFS or Lustre.

Note: NFS is not strongly consistent and cannot be used for the hosts file!

GekkoFS daemon start and shut down

tl;dr example: <install_path>/bin/gkfs_daemon -r <fs_data_path> -m <pseudo_gkfs_mount_dir_path> -H <hostsfile_path>

Run the GekkoFS daemon on each node specifying its locally used directory where the file system data and metadata is stored (-r/--rootdir <fs_data_path>), e.g., the node-local SSD; 2. the pseudo mount directory used by clients to access GekkoFS (-m/--mountdir <pseudo_gkfs_mount_dir_path>); and 3. the hostsfile path (-H/--hostsfile <hostfile_path>).

Further options are available:

Allowed options
Usage: src/daemon/gkfs_daemon [OPTIONS]

Options:
  -h,--help                   Print this help message and exit
  -m,--mountdir TEXT REQUIRED Virtual mounting directory where GekkoFS is available.
  -r,--rootdir TEXT REQUIRED  Local data directory where GekkoFS data for this daemon is stored.
  -s,--rootdir-suffix TEXT    Creates an additional directory within the rootdir, allowing multiple daemons on one node.
  -i,--metadir TEXT           Metadata directory where GekkoFS RocksDB data directory is located. If not set, rootdir is used.
  -l,--listen TEXT            Address or interface to bind the daemon to. Default: local hostname.
                              When used with ofi+verbs the FI_VERBS_IFACE environment variable is set accordingly which associates the verbs device with the network interface. In case FI_VERBS_IFACE is already defined, the argument is ignored. Default 'ib'.
  -H,--hosts-file TEXT        Shared file used by deamons to register their endpoints. (default './gkfs_hosts.txt')
  -P,--rpc-protocol TEXT      Used RPC protocol for inter-node communication.
                              Available: {ofi+sockets, ofi+verbs, ofi+psm2} for TCP, Infiniband, and Omni-Path, respectively. (Default ofi+sockets)
                              Libfabric must have enabled support verbs or psm2.
  --auto-sm                   Enables intra-node communication (IPCs) via the `na+sm` (shared memory) protocol, instead of using the RPC protocol. (Default off)
  --clean-rootdir             Cleans Rootdir >before< launching the deamon
  -c,--clean-rootdir-finish   Cleans Rootdir >after< the deamon finishes
  -d,--dbbackend TEXT         Metadata database backend to use. Available: {rocksdb, parallaxdb}
                              RocksDB is default if not set. Parallax support is experimental.
                              Note, parallaxdb creates a file called rocksdbx with 8GB created in metadir.
  --parallaxsize TEXT         parallaxdb - metadata file size in GB (default 8GB), used only with new files
  --enable-collection         Enables collection of general statistics. Output requires either the --output-stats or --enable-prometheus argument.
  --enable-chunkstats         Enables collection of data chunk statistics in I/O operations.Output requires either the --output-stats or --enable-prometheus argument.
  --output-stats TEXT         Creates a thread that outputs the server stats each 10s to the specified file.
  --enable-prometheus         Enables prometheus output and a corresponding thread.
  --prometheus-gateway TEXT   Defines the prometheus gateway <ip:port> (Default 127.0.0.1:9091).
  --version                   Print version and exit.

It is possible to run multiple independent GekkoFS instances on the same node. Note, that when these GekkoFS instances are part of the same file system, use the same rootdir with different rootdir-suffixes.

Shut it down by gracefully killing the process (SIGTERM).

Use the GekkoFS client library

tl;dr example:

export LIBGKFS_ HOSTS_FILE=<hostfile_path>
LD_PRELOAD=<install_path>/lib64/libgkfs_intercept.so cp ~/some_input_data <pseudo_gkfs_mount_dir_path>/some_input_data
LD_PRELOAD=<install_path>/lib64/libgkfs_intercept.so md5sum ~/some_input_data <pseudo_gkfs_mount_dir_path>/some_input_data

Clients read the hostsfile to determine which daemons are part of the GekkoFS instance. Because the client is an interposition library that is loaded within the context of the application, this information is passed via the environment variable LIBGKFS_HOSTS_FILE pointing to the hostsfile path. The client library itself is loaded for each application process via the LD_PRELOAD environment variable intercepting file system related calls. If they are within (or hierarchically under) the GekkoFS mount directory they are processed in the library, otherwise they are passed to the kernel.

Note, if LD_PRELOAD is not pointing to the library and, hence the client is not loaded, the mounting directory appears to be empty.

For MPI application, the LD_PRELOAD variable can be passed with the -x argument for mpirun/mpiexec.

Run GekkoFS daemons on multiple nodes (beta version!)

The scripts/run/gkfs script can be used to simplify starting the GekkoFS daemon on one or multiple nodes. To start GekkoFS on multiple nodes, a Slurm environment that can execute srun is required. Users can further modify scripts/run/gkfs.conf to mold default configurations to their environment.

The following options are available for scripts/run/gkfs:

usage: gkfs [-h/--help] [-r/--rootdir <path>] [-m/--mountdir <path>] [-a/--args <daemon_args>] [-f/--foreground <false>]
        [--srun <false>] [-n/--numnodes <jobsize>] [--cpuspertask <64>] [--numactl <false>] [-v/--verbose <false>]
        {start,stop}


    This script simplifies the starting and stopping GekkoFS daemons. If daemons are started on multiple nodes,
    a Slurm environment is required. The script looks for the 'gkfs.conf' file in the same directory where
    additional permanent configurations can be set.

    positional arguments:
            command                 Command to execute: 'start' and 'stop'

    optional arguments:
            -h, --help              Shows this help message and exits
            -r, --rootdir <path>    Providing the rootdir path for GekkoFS daemons.
            -m, --mountdir <path>   Providing the mountdir path for GekkoFS daemons.
            -a, --args <daemon_arguments>
                                    Add various additional daemon arguments, e.g., "-l ib0 -P ofi+psm2".
            -f, --foreground        Starts the script in the foreground. Daemons are stopped by pressing 'q'.
            --srun                  Use srun to start daemons on multiple nodes.
            -n, --numnodes <n>      GekkoFS daemons are started on n nodes.
                                    Nodelist is extracted from Slurm via the SLURM_JOB_ID env variable.
            --cpuspertask <#cores>  Set the number of cores the daemons can use. Must use '--srun'.
            --numactl               Use numactl for the daemon. Modify gkfs.conf for further numactl configurations.
            -c, --config            Path to configuration file. By defaults looks for a 'gkfs.conf' in this directory.
            -v, --verbose           Increase verbosity

Logging

The following environment variables can be used to enable logging in the client library: LIBGKFS_LOG=<module> and LIBGKFS_LOG_OUTPUT=<path/to/file> to configure the output module and set the path to the log file of the client library. If not path is specified in LIBGKFS_LOG_OUTPUT, the client library will send log messages to /tmp/gkfs_client.log.

The following modules are available:

• none: don't print any messages
• syscalls: Trace system calls: print the name of each system call, its arguments, and its return value. All system calls are printed after being executed save for those that may not return, such as execve(), execve_at(), exit(), and exit_group(). This module will only be available if the client library is built in Debug mode.
• syscalls_at_entry: Trace system calls: print the name of each system call and its arguments. All system calls are printed before being executed and therefore their return values are not available in the log. This module will only be available if the client library is built in Debug mode.
• info: Print information messages.
• critical: Print critical errors.
• errors: Print errors.
• warnings: Print warnings.
• mercury: Print Mercury messages.
• debug: Print debug messages. This module will only be available if the client library is built in Debug mode.
• most: All previous options combined except syscalls_at_entry. This module will only be available if the client library is built in Debug mode.
• all: All previous options combined.
• trace_reads: Generate log line with extra information in read operations for guided distributor
• help: Print a help message and exit.

When tracing sytem calls, specific syscalls can be removed from log messages by setting the LIBGKFS_LOG_SYSCALL_FILTER environment variable. For instance, setting it to LIBGKFS_LOG_SYSCALL_FILTER=epoll_wait,epoll_create will filter out any log entries from the epoll_wait() and epoll_create() system calls.

Additionally, setting the LIBGKFS_LOG_OUTPUT_TRUNC environment variable with a value different from 0 will instruct the logging subsystem to truncate the file used for logging, rather than append to it.

For the daemon, the GKFS_DAEMON_LOG_PATH=<path/to/file> environment variable can be provided to set the path to the log file, and the log module can be selected with the GKFS_DAEMON_LOG_LEVEL={off,critical,err,warn,info,debug,trace} environment variable.

Miscellaneous

External functions

GekkoFS allows to use external functions on your client code, via LD_PRELOAD. Source code needs to be compiled with -fPIC. We include a pfind io500 substitution, examples/gfind/gfind.cpp and a non-mpi version examples/gfind/sfind.cpp

Data distributors

The data distribution can be selected at compilation time, we have 2 distributors available:

Simple Hash (Default)

Chunks are distributed randomly to the different GekkoFS servers.

Guided Distributor

The guided distributor allows defining a specific distribution of data on a per directory or file basis. The distribution configurations are defined within a shared file (called guided_config.txt henceforth) with the following format: <path> <chunk_number> <host>

To enable the distributor, the following CMake compilation flags are required:

• GKFS_USE_GUIDED_DISTRIBUTION ON
• GKFS_USE_GUIDED_DISTRIBUTION_PATH <path_guided_config.txt>

To use a custom distribution, a path needs to have the prefix # (e.g., #/mdt-hard 0 0), in which all the data of all files in that directory goes to the same place as the metadata. Note, that a chunk/host configuration is inherited to all children files automatically even if not using the prefix. In this example, /mdt-hard/file1 is therefore also using the same distribution as the /mdt-hard directory. If no prefix is used, the Simple Hash distributor is used.

Guided configuration file

Creating a guided configuration file is based on an I/O trace file of a previous execution of the application. For this the trace_reads tracing module is used (see above).

The trace_reads module enables a TRACE_READS level log at the clients writing the I/O information of the client which is used as the input for a script that creates the guided distributor setting. Note that capturing the necessary trace records can involve performance degradation. To capture the I/O of each client within a SLURM environment, i.e., enabling the trace_reads module and print its output to a user-defined path, the following example can be used: srun -N 10 -n 320 --export="ALL" /bin/bash -c "export LIBGKFS_LOG=trace_reads;LIBGKFS_LOG_OUTPUT=${HOME}/test/GLOBAL.txt;LD_PRELOAD=${GKFS_PRLD} <app>"

Then, the examples/distributors/guided/generate.py scrpt is used to create the guided distributor configuration file:

• python examples/distributors/guided/generate.py ~/test/GLOBAL.txt >> guided_config.txt

Finally, modify guided_config.txt to your distribution requirements.

Metadata Backends

There are two different metadata backends in GekkoFS. The default one uses rocksdb, however an alternative based on PARALLAX from FORTH is available. To enable it use the -DGKFS_ENABLE_PARALLAX:BOOL=ON option, you can also disable rocksdb with -DGKFS_ENABLE_ROCKSDB:BOOL=OFF.

Once it is enabled, --dbbackend option will be functional.

Statistics

GekkoFS daemons are able to output general operations (--enable-collection) and data chunk statistics (--enable-chunkstats) to a specified output file via --output-stats <FILE>. Prometheus can also be used instead or in addition to the output file. It must be enabled at compile time via the CMake argument -DGKFS_ENABLE_PROMETHEUS and the daemon argument --enable-prometheus. The corresponding statistics are then pushed to the Prometheus instance.

Advanced experimental features

Rename

-DGKFS_RENAME_SUPPORT allows the application to rename files. This is an experimental feature, and some scenarios may not work properly. Support for fstat in renamed files is included.

This is disabled by default.

Acknowledgment

This software was partially supported by the EC H2020 funded NEXTGenIO project (Project ID: 671951, www.nextgenio.eu).

This software was partially supported by the ADA-FS project under the SPPEXA project (http://www.sppexa.de/) funded by the DFG.

This software is partially supported by the FIDIUM project funded by the DFG.

This software is partially supported by the ADMIRE project (https://www.admire-eurohpc.eu/) funded by the European Union’s Horizon 2020 JTI-EuroHPC Research and Innovation Programme (Grant 956748).