Variable Name
Options Purpose
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.
6.1.5
Modes
6.1.5.1 About DVS Modes
There are two primary ways to use Cray DVS: in serial mode or parallel mode, as indicated in the following table.
In serial mode, one DVS server on a Cray service node projects a file system to multiple compute node clients. In
parallel mode, multiple DVS servers—in configurations that vary in purpose, layout, and performance—project a
file system to multiple compute node clients.
Table 15. Cray DVS Access Modes
Mode
Access Level
Pattern
Serial
Read/Write
Many clients, one server
Parallel
Read/Write
Many clients, many servers
DVS mode is not selected by a switch, but rather by configuration. It is determined by the system administrator's
choice of DVS mount point options. A DVS mode is really just the name given to a collection of mount options
chosen to achieve a particular goal. Users cannot choose among DVS modes unless the system administrator
has configured the system to make more than one mode available. A system administrator can make several
DVS modes available on the same compute node by mounting a file system with different mount point options on
different mount points on that compute node. This table shows the rationale and an example mount entry for each
DVS mode.
Mode
Rationale
Example Configuration Settings
Serial
Simplest implementation of DVS. Only option if
no cluster/shared file system available.
servers: r0s0c1n1
options: maxnodes=1
Cluster
Parallel
Often used for a large file system, must be a
shared file system such as GPFS (Spectrum
Scale). Can distribute file I/O and metadata
operations among several servers to avoid
overloading any one server and to speed up
operations. I/O for a single file goes only to the
chosen server.
servers: r0s1c1n1, r0s2c1n2,
r0s2c0n1
options: maxnodes=1
Stripe Parallel Used to distribute file I/O load at the granularity
of a block of data within a file. Adds another level
servers: r0s1c1n1, r0s2c1n2,
r0s2c0n1
options: maxnodes=3
Cray DVS
S3016
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