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LibLustre How-To Guide
For most Lustre versions, a library version of the Lustre client file system (liblustre) is available. Liblustre gives a user application (linked with the library) access to Lustre file systems, without needing to mount Lustre (VFS) on the client. The key goals for the library are to provide a portable mechanism to access Lustre from different POSIX-compliant operating systems, and to provide access from microkernel-based systems.
Currently, liblustre is still under development and only works on linux (i386 & x86_64, not tested on ia64).
In this document, we will discuss how to use liblustre.
Note: liblustre is not required or even recommended for running Lustre on Linux. Most users will not use liblustre. Instead, you should use the Lustre (VFS) client file system to mount Lustre directly. liblustre does NOT support multi-threaded applications.
Generally speaking, liblustre implements the Lustre client filesystem in user space. The liblustre component links LNET and libsysio together to form a shared library which can be used by applications to perform file I/O.
Building Clients and Servers for liblustre
When using liblustre, servers are first built/configured in the usual way as described in Building and Installing Lustre from Source Code. By default, liblustre is built unless "./configure --disable-liblustre" is specified.
The following liblustre files are located in lustre/liblustre:
How to Use liblustre
First, you must configure the networking on Lustre servers (MDS/OSTs) to accept connections on insecure ports. For example, add options lnet networks=tcp(eth0) accept=all to /etc/modprobe.conf before mounting the server(s) as usual. If you do not have any Lustre filesystem, the llmount.sh script will format temporary MDT and OST filesystems and start up MDS, OSS, and clients on that machine. You should umount the Lustre client at /mnt/lustre to avoid confusion between the liblustre client and the normal VFS client if you are also using that node for the liblustre client.
liblustre needs to know the mount target before connecting to a Lustre server. The format is similar to the following:
- mgs_nid is the actual hostname of the MGS (or IP address if you do not have proper name resolution set up).
- profile_name is the profile name of the client mount point, also called the filesystem name in many configurations.
For additional information on mount target, refer to Lustre documentation. This can be passed to most liblustre programs via the environment variable LIBLUSTRE_MOUNT_TARGET.
There is a statically built-in liblustre test program lustre/liblustre/tests/sanity that is also included in the lustre-tests RPM package. You can use this test to verify if liblustre is working properly:
sanity --target mgs_nid:/profile_name
How It Works
If we run an existing program, e.g. iozone, then we will use LD_PRELOAD to load liblustre.so first. The start function of liblustre.so will mount a lustre partition on certain directories, e.g. /mnt/lustre. Furthermore, following loaded iozone's functions calls such as open, read, write, etc. will dynamically linked with implementations in liblustre.so, instead of libc in the usual case. Thus, we can intercept filesystem-related system calls and translate them into Lustre commands.
Necessary Environmental Variables
There is a simple script lustre/utils/lrun which set some environment variables:
- mount point
This is where liblustre mounts the remote Lustre filesystem. The default location is /mnt/lustre. Make sure this directory exists on the client system.
- mount target
Before using liblustre, you need to fill in the mount target (e.g. mdshost:/profile_name).
- shared library
Make sure you have installed lustre/liblustre/liblustre.so in this location.
- server port
This is optional, necessary only when the Lustre server doesn't listen on the default port (e.g. server uses the lnet option "accept_port" to change its port). It's only meaningful for the socklnd (TCP network).
- other LNET options
You'd need to set LNET_ROUTES for the liblustre client to use routing to access the remote filesystem.
Running Programs over liblustre
Until now, only a small number of applications have been tested with liblustre:
And also several standard UNIX commands:
You need to prepend 'lrun' before the programs that you intend to run:
lrun iozone -f /mnt/lustre/ioz_testfile -r 256k -s 1g lrun mkdir /mnt/lustre/testdir lrun touch /mnt/lustre/testdir/testfile lrun cp /etc/fstab /mnt/lustre/testdir lrun ls /mnt/lustre/testdir lrun find /mnt/lustre/ lrun .....
liblustre is not widely tested as part of Lustre release testing, and is currently maintained only as a courtesy to the Lustre community.