Mode
Rationale
Example Configuration Settings
of parallelism to better distribute the load. I/O for
a single file may go to multiple servers.
Atomic Stripe
Parallel
Used when stripe parallel makes sense and
POSIX read/write atomicity required.
servers: r0s1c1n1, r0s2c1n2,
r0s2c0n1
options: maxnodes=3,atomic
Loadbalance
Used for near-optimal load distribution when a
read-only file system is being used. By default,
enables
readonly
and sets
cache=1
,
failover=1
,
maxnodes=1
, and
hash_on_nid=0
.
servers: r0s1c1n1, r0s2c1n2,
r0s2c0n1
loadbalance: true
Serial, cluster parallel, and atomic stripe parallel modes all adhere to POSIX read/write atomicity rules, but stripe
parallel mode does not. POSIX read/write atomicity guarantees that all bytes associated with a read or write are
not interleaved with bytes from other read or write operations.
6.1.5.2 About DVS Serial Mode
Serial mode is the simplest implementation of DVS, where each file system is projected from a single DVS server
to multiple clients (see figure). DVS can project multiple file systems in serial mode by assigning a new or existing
DVS server to each additional file system in serial access mode and entering the appropriate mount point on the
clients. The following example mount entry contains the mount options essential for serial mode: a single
nodename
and
maxnodes=1
.
mount -o nodename=server1, maxnodes=1
DVS serial mode adheres to POSIX read/write atomicity rules.
Figure 32. Cray DVS Serial Access Mode
Cray System
DVS Client
DVS Client
Application
DVS Client
FS Client
FS Server
Disk FS
DVS Server
Application
DVS Client
Application
Application
Cray DVS
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