User`s guide

Cray XMT™ Programming Environment User’s Guide

The easiest way to understand this is to imagine data going to a file from the

application. In this case, the data is copied by each compute node into the FIO

transport and sent to its corresponding

fsworker on a login node in the Linux

service partition. Each fsworker then uses Linux system calls to write data into

the Lustre file, which results in the data moving across the Portals transport from the

Fibre Channel (FC) to the actual storage device.

Moving data from a file to the application simply reverses the order of the stages and

the direction of the data flow through each stage, ultimately resulting in data being

copied from compute nodes into the application's global memory buffer.

6.2 The Snapshot Library Interface

Note: Effective with Cray XMT version 2.0 the snap_* functions are replaced by

dslr_* equivalents. The snap_* functions are deprecated and will be removed

in a future release.

The snapshot library interface consists of these functions:

dslr_snapshot

Copies data in parallel from a buffer in the application to a file on

the service partition.

dslr_restore

Copies data in parallel from a file on the service partition to a buffer

in the application.

dslr_pread Allows the application to specify an offset into a file from which to

read data. Does not move data in parallel.

dslr_pwrite

Allows the application to specify an offset into a file at which to

write data. Does not move data in parallel.

dslr_stat Allows the application to obtain file status from a file, similar to the

stat function.

dslr_truncate

Truncates a file to a specified length.

For more information on any of these functions, see the associated man page.

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