ZOID

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Introduction

ZOID is an I/O forwarding component of the ZeptoOS project. Any communication between the compute nodes and I/O nodes (job management, file I/O, sockets) is facilitated by ZOID.

ZOID infrastructure consists of:

• Multithreaded zoid daemon on the I/O nodes which performs I/O forwarding for the compute nodes and which also communicates with the service node to perform job management,
• control daemon on the compute nodes which is responsible for job management tasks such as launching application processes, for the forwarding of stdin/out/err data, and for forwarding of IP packets,
• zoid-fuse daemon on the compute nodes which performs file I/O forwarding for POSIX-compliant applications.

User interface

User script

Right before a job starts running, and right after the last process of a job has terminated, ZOID daemon attempts to invoke a user script on I/O nodes. By default, the daemon invokes $HOME/zoid-user-script.sh (this pathname can be changed by an administrator). A single parameter is passed to the script: 1 at the job startup, and 0 at the termination.

Information about the job will be passed to the script in the following environment variables:

ZOID_JOB_EXEC

name of the job executable,

ZOID_JOB_ARGS

job arguments, separated by a :

ZOID_JOB_ENV

job environment variables, separated by a :

ZOID_JOB_ID

BG/P control system job id (Note: this is generally different from the Cobalt job ID; see FAQ for the latter),

ZOID_JOB_GLOBAL_SIZE

number of processes in the job (size of MPI_COMM_WORLD),

ZOID_JOB_LOCAL_SIZE

number of job processes handled by this I/O node,

ZOID_JOB_MODE

0 for SMP, 1 for VN, and 2 for DUAL,

SHELL, PATH, USER, and HOME

will also be set...

File broadcast

A /bin.rd/f2cn command is available on the I/O nodes for a very efficient (hardware-assisted) broadcasting of files to all the compute nodes handled by the given I/O node.

The command takes two arguments:

• absolute pathname to the input file on the I/O node,
• absolute pathname to the output file on the compute nodes.

The input file does not need to be physically on the I/O node; it can be on a network filesystem mounted on the node. The file will be created in the ramdisk of each compute node.

The throughput is in practice limited by how fast the input file can be read; we have seen results in excess of 300 MB/s for files residing in the I/O node ramdisk.

Note: all the compute nodes in the pset must be up and running. Do not use this command on incomplete partitions (e.g., a one-process job on a 64-node partition); you will likely hang the ZOID daemon if you try.

Performance counters

A /bin.rd/statquery command is available on the I/O nodes for obtaining the performance counters of the I/O daemon.

The command takes a single optional argument:

• the interval between successive queries, in seconds.

If the argument is not provided, the command will terminate after the first query.

Here is the sample output generated:

Administrator interface

Command line options

-u

Programmer interface

Building a new plugin

Replacement libc?

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