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Storage Resource Managers (SRMs) are middleware components whose function is to provide dynamic space allocation and file management on shared storage components on the Grid. SRMs support protocol negotiation and reliable replication mechanism. The SRM specification standardizes the interface, thus allowing for a uniform access to heterogeneous storage elements.The SRM standard allows independent institutions to implement their own SRMs. SRMs leave the policy decision to be made independently by each implementation at each site. Resource Reservations made through SRMs have limited lifetimes and allow for automatic collection of unused resources thus preventing clogging of storage systems with “forgotten” files.
The storage systems can be classified on basis of their longevity and persistence of the data they store. Data can be considered to be temporary and permanent. For example disc caches might allow for spontaneous deletion of the files, while deletion of the file stored in a robotic tape storage can be very problematic. To support these notions, SRM defines three types of files and spaces: Volatile, Durable and Permanent. Volatile files can be removed by the system to make space for new files upon the expiration of its lifetime. Permanent files are expected to exist in the storage system for the lifetime of the storage system, unless explicitly deleted by the user. Finally Durable files have a both the lifetime associated with them and a mechanism of notification of owners and administrators of lifetime expiration but can not be deleted automatically by the system and require explicit removal.
SRM
interface consists of the five categories of functions: Space
Management, Data Transfer, Request Status, Directory and Permission
Functions. Among the functions worth mentioning are srmReserveSpace
which creates advanced space reservation with a user specified
lifetime, and identified by a unique space token. The space token can
later be utilized for storing files via srmPrepareToPut,
srmPrepareToGet and srmCopy functions. For example srmPrepareToPut
will take the list of files, file sizes, list client supported
transfer protocols and space tokens. SRM interface utilizes Grid
Security Infrastructure (GSI) for authentications. SRM service is a
Web Service implementation of a published WSDL document. Fermilab
SRM is based on and is an integral part of the dCache Distributed
Disk Cache coupled with Enstore Tape Storage System.
The Fermilab SRM client tools package "f-srmcp" provides the ability to interact with SRM services meeting the same API specification. These client tools are not dCache-specific; they are interoperable with other services. No services have to be installed to use these clients. It is assumed that the installation platform already has a Java run-time, and, if desired to be used, Globus tools. In Fermilab UPS/UPD, this is equivalent to the "srmcp" package.
| Most SRM documents can be found at SRM Working Group page |
| CHEP04 Conference Paper (PDF) (MS WORD) |
| SRM Presentation to UK National eScience Centre (NeSC)r (PDF) (MS PowerPoint) |
| Twelfth
NASA Goddard and Twenty First IEEE Conference on Mass Storage Systems
and Technologies Abstract (PDF) (MS WORD) Presentation (PDF) (MS PowerPoint) |
| Computer Division SRM review presentation(pdf) (MS PowerPoint) |
Fermilab Reference Implementation of Unix File System SRM
For assistance contact helpdesk@fnal.gov.
Information compiled and maintained by Timur Perelmutov ; last modified on 04/22/04 .
(Address comments about page to timur@fnal.gov.)
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