Red Hat GLOBAL FILE SYSTEM 4.7 Guía de usuario descargar pdf (Pagina 96)

User interaction with Lustre file systems6–12

6.3.5 Using a Lustre file system in the PATH variable

HP strongly recommends that you do not add a Lustre file system into the PATH variable as a means of

executing binaries on the Lustre file system. Instead, use full paths for naming those binaries.

If it is not possible to exclude a Lustre file system from the PATH variable, the Lustre file system must come as

late in the PATH definition as possible, to avoid a lookup penalty on local binary execution. Also, do not

specify the same Lustre path more than once.

6.3.6 Optimizing the use of the GNU ls command on Lustre file systems

On modern Linux systems, the GNU ls command often uses colorization by default to visually highlight the

file type; this is especially true if the command is run within a terminal session. This is because the default

shell profile initializations usually contain an alias directive similar to the following for the ls command:

alias ls='ls --color=tty'

However, running the ls command in this way for files on a Lustre file system requires a stat() call to be

used to determine the file type. This can result in a performance overhead, because the stat() call always

needs to determine the size of a file, and that in turn means that the client node must query the object size

of all the backing objects that make up a file.

As a result of the default colorization setting, running a simple ls command on a Lustre file system often

takes as much time as running the ls command with the -l option. (The same is true if the -F, -p, or the

--classify option, or any other option that requires information from a stat() call, is used.)

If you want your ls commands to avoid incurring this performance overhead, add an alias directive similar

to the following to your shell startup script:

alias ls='ls --color=none'

6.3.7 Using st_blksize to determine optimum I/O block size

Many legacy applications use the st_blksize of the stat structure returned from the stat() system

call to determine the optimum I/O block size for operations. In the case of Lustre, this field contains the stripe

size of the file. If you intend to read small amounts of data from a file (for example, 4KB), ensure that your

application is not reading more data than it requires. You can check the size of the I/O blocks issued by

your application by using an application such as strace to examine the return values of the read system

calls.

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Red Hat GLOBAL FILE SYSTEM 4.7 Guía de usuario Pagina 96