accessmethods

AccessMethods page for ClusterGate

Here we plan to mention various access methods to large volume of data.

XrootD the Next Generation Root File Server
dCacheThe goal of this project is to provide a system for storing and retrieving huge amounts of data, distributed among a large number of heterogenous server nodes, under a single virtual filesystem tree with a variety of standard access methods. Depending on the Persistency Model, dCache provides methods for exchanging data with backend (tertiary) Storage Systems as well as space management, pool attraction, dataset replication, hot spot determination and recovery from disk or node failures. Connected to a tertiary storage system, the cache simulates unlimited direct access storage space. Dataexchanges to and from the underlying HSM are performed automatically and invisibly to the user. Filesystem namespace operations may be performed through a standard nfs(2) interface.
GA - Global Arrays. Global Arrays have been designed to complement rather than substitute for the message-passing programming model. The programmer is free to use both the shared-memory and message-passing paradigms in the same program, and to take advantage of existing message-passing software libraries. Global Arrays are compatible with the Message Passing Interface (MPI).
Global Arrays The Global Arrays (GA) toolkit provides an efficient and portable .shared-memory. programming interface for distributed-memory computers. Each process in a MIMD parallel program can asynchronously access logical blocks of physically distributed dense multi-dimensional arrays, without need for explicit cooperation by other processes. Unlike other shared-memory environments, the GA model exposes to the programmer the non-uniform memory access (NUMA) characteristics of the high performance computers and acknowledges that access to a remote portion of the shared data is slower than to the local portion. The locality information for the shared data is available, and a direct access to the local portions of shared data is provided. More information on these can be found on the
NBD Network Block Device (TCP version) What is it: With this thing compiled into your kernel, Linux can use a remote server as one of its block devices. Every time the client computer wants to read /dev/nd0, it will send a request to the server via TCP, which will reply with the data requested. This can be used for stations with low disk space (or even diskless - if you boot from floppy) to borrow disk space from other computers. Unlike NFS, it is possible to put any file system on it. But (also unlike NFS), if someone has mounted NBD read/write, you must assure that no one else will have it mounted.
DRBD is a block device which is designed to build high availability clusters. This is done by mirroring a whole block device via (a dedicated) network. You could see it as a network raid-1.
DPM The Disk Pool Manager (DPM) is a lightweight solution for disk storage management. If offers the required SRM interfaces, hopefully without being complicated by other modes of access or complications such as tape storage systems. It has been developed at CERN
SRM Working Group for standards on storage resource management
SRB The SDSC Storage Resource Broker (SRB) is client-server middleware that provides a uniform interface for connecting to heterogeneous data resources over a network and accessing replicated data sets. SRB, in conjunction with the Metadata Catalog (MCAT), provides a way to access data sets and resources based on their attributes and/or logical names rather than their names or physical locations.

Andrey Ye. Shevel