Veritas Storage Foundation 5.1 SP1 Cluster File System Administrator"s Guide (5900-1738, April 2011)

Traditionally, the entire file is locked to perform I/O to a small region. To support

parallel I/O, SFCFS locks ranges in a file that correspond to I/O requests. Two I/O

requests conflict if at least one is a write request, and the I/O range of the request

overlaps the I/O range of the other.

The parallel I/O feature enables I/O to a file by multiple threads concurrently, as

long as the requests do not conflict. Threads issuing concurrent I/O requests could

be executing on the same node, or on different nodes in the cluster.

An I/O request that requires allocation is not executed concurrently with other

I/O requests. Note that when a writer is extending the file and readers are lagging

behind, block allocation is not necessarily done for each extending write.

Predetermine the file size and preallocate the file to avoid block allocations during

I/O. This improves the concurrency of applications performing parallel I/O to the

file. Parallel I/O also avoids unnecessary page cache flushes and invalidations

using range locking, without compromising the cache coherency across the cluster.

For applications that update the same file from multiple nodes, the -nomtime

mount option provides further concurrency. Modification and change times of

the file are not synchronized across the cluster, which eliminates the overhead

of increased I/O and locking. The timestamp seen for these files from a node may

not have the time updates that happened in the last 60 seconds.

I/O error handling policy

I/O errors can occur for several reasons, including failures of Fibre Channel links,

host-bus adapters, and disks. SFCFS disables the file system on the node

encountering I/O errors. The file system remains available from other nodes.

After the hardware error is fixed (for example, the Fibre Channel link is

reestablished), the file system can be force unmounted and the mount resource

can be brought online from the disabled node to reinstate the file system.

Recovering for I/O failures

The disabled file system can be restored by a force unmount and the resource will

be brought online without rebooting, which also brings the shared disk group

resource online.

Note: If the jeopardy condition is not fixed, the nodes are susceptible to leaving

the cluster again on subsequent node failure.

See the Veritas Cluster Server User’s Guide.

Storage Foundation Cluster File System architecture

I/O error handling policy