DocIOSystems

I/O system types

Overview

This document describes the configuration types for I/O systems in a SLASH2 deployment. An I/O system in SLASH2 comprises a logical set of one or more storage nodes.

For more information about each IOS type, consult the slcfg(5) manual.

Standalone I/O system

The standalone IOS is the most basic form of a SLASH2 I/O system:

resource lemon {
	desc	= "Stand-alone I/O server";
	type	= standalone_fs;
	id	= 2;
	nids	= lemon.psc.edu;
	fsroot	= /local/s2io;
}

The main parameter fsroot specifies the path to the underlying storage which is to be exported into the SLASH2 deployment. The SLASH2 I/O daemon will expect to find its private internal directory hierarchy at this location. Currently, the SLASH2 I/O service sliod(8) operates on a single file system root.

Archival I/O system

The archival I/O type is used for systems which frequently encounter long delays on read such as a tape archiver or other type of jukebox system. The primary difference between archival and standalone is internal timeout mechanism for network requests. Otherwise, the configuration is the same:

resource tapearchiver {
	desc	= "Archival I/O server";
	type	= archival_fs;
	id	= 3;
	nids	= turtle.psc.edu;
	fsroot	= /tape;
}

Cluster "non shared" I/O system (CNOS)

The CNOS I/O type is used for binding logical sets of standalone nodes into a "single" resource (for organizational purposes). For instance, 4 I/O nodes, each with local storage, may be bound into a "single" I/O resource for easier facilitation of striping and load balancing:

site PSC {
	resource ios0 {
		desc	= "I/O server 0";
		type	= standalone_fs;
		id	= 100;
		nids	= ios0.psc.edu;
		fsroot	= /local;
	}

	resource ios1 {
		desc	= "I/O server 1";
		type	= standalone_fs;
		id	= 101;
		nids	= ios1.psc.edu;
		fsroot	= /local;
	}

	resource ios2 {
		desc	= "I/O server 2";
		type	= standalone_fs;
		id	= 102;
		nids	= ios2.psc.edu;
		fsroot	= /local;
	}

	resource ios3 {
		desc	= "I/O server 3";
		type	= standalone_fs;
		id	= 103;
		nids	= ios3.psc.edu;
		fsroot	= /local;
	}

	resource ios_cnos {
		desc	= "cluster no share of ios0-3";
		type	= cluster_noshare_lfs;
		id	= 1000;
		ios	= ios0@PSC, ios1@PSC, ios2@PSC, ios3@PSC;
	}

	...
}

When a client selects ios_cnos@PSC as its preferred I/O system, writes will be load balanced amongst the available members of the CNOS. Selection of the preferred I/O system is done via slcfg(5) configuration or during runtime via msctl(8):

# msctl -p sys.pref_ios=ios_cnos@PSC