DVS Environment Variables

By default, user environment variables allow client override of mount options specified during configuration.

By default, user environment variables allow client override of options specified during configuration and are evaluated whenever a file is opened by DVS. However, if the nouserenv option is included in the options setting of the client_mount configuration setting, then user environment variables are disabled for that client mount.

The following environment variables are for use in the default case:

Cray DVS User Environment Variables

Variable Name	Options	Purpose
`DVS_ATOMIC`	`on\|off`	Overrides the `atomic` or `noatomic` mount options.
`DVS_BLOCKSIZE`	`n`	A nonzero number, `n` overrides the `blksize` mount option.
`DVS_CACHE`	`on\|off`	Overrides the `cache` or `nocache` mount options. Exercise caution if using this variable. Allowing an application to bypass cached data on the file system could lead to coherency issues between the local cached file data and what is read from the backing file system. Allowing a file to read data from the backing store could also cause issues with an inode shared between cached and uncached open file handles by updating inode attributes and putting the inode out of sync with the current state of cached data. For additional cautions about write caching, see "Client-side Write-back Caching may not be Suitable for all Applications" in DVS Client-side Write-back Caching can Yield Performance Gains.
`DVS_CACHE_READ_SZ`	`n`	A positive integer, `n` overrides the `cache_read_sz` mount option.
`DVS_CLOSESYNC`	`on\|off`	Overrides the `closesync` or `noclosesync` mount options. Note: Periodic sync functions similarly to the DVS `closesync` mount option, but it is more efficient and is enabled by default. Cray recommends not using `closesync` or this associated environment variable.
`DVS_DATASYNC`	`on\|off`	Overrides the `datasync` or `nodatasync` mount options. Note: Setting `DVS_DATASYNC` to `on` can slow down an application considerably. The periodic sync feature, enabled by default, is a better way to synchronize data. See Periodic Sync Promotes Data and Application Resiliency.
`DVS_DEFEROPENS`	`on\|off`	Overrides the `deferopens` or `nodeferopens` mount options.
`DVS_KILLPROCESS`	`on\|off`	Overrides the `killprocess` or `nokillprocess` mount options.
`DVS_MAXNODES`	`n`	A nonzero number, `n` overrides the `maxnodes` mount option. The specified value of `maxnodes` must be greater than zero and less than or equal to the number of server nodes specified on the mount, otherwise the variable has no effect.