233 lines
6.5 KiB
Groff
233 lines
6.5 KiB
Groff
.\" Copyright (c) 2010 The FreeBSD Foundation
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.\" All rights reserved.
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.\"
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.\" This software was developed by Pawel Jakub Dawidek under sponsorship from
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.\" the FreeBSD Foundation.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd February 1, 2010
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.Dt HASTD 8
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.Os
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.Sh NAME
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.Nm hastd
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.Nd "Highly Available Storage daemon"
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.Sh SYNOPSIS
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.Nm
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.Op Fl dFh
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.Op Fl c Ar config
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.Op Fl P Ar pidfile
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.Sh DESCRIPTION
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The
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.Nm
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daemon is responsible for managing highly available GEOM providers.
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.Pp
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.Nm
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allows to transparently store data on two physically separated machines
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connected over the TCP/IP network.
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Only one machine (cluster node) can actively use storage provided by
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.Nm .
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This machine is called primary.
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The
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.Nm
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daemon operates on block level, which makes it transparent to file
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systems and applications.
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.Pp
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There is one main
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.Nm
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daemon which starts new worker process as soon as a role for the given
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resource is changed to primary or as soon as a role for the given
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resource is changed to secondary and remote (primary) node will
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successfully connect to it.
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Every worker process gets a new process title (see
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.Xr setproctitle 3 ) ,
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which describes its role and resource it controls.
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The exact format is:
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.Bd -literal -offset indent
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hastd: <resource name> (<role>)
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.Ed
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.Pp
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If (and only if)
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.Nm
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operates in primary role for the given resource, a corresponding
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.Pa /dev/hast/<name>
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disk-like device (GEOM provider) is created.
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File systems and applications can use this provider to send I/O
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requests to.
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Every write, delete and flush operation
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.Dv ( BIO_WRITE , BIO_DELETE , BIO_FLUSH )
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is sent to the local component and replicated on the remote (secondary) node
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if it is available.
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Read operations
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.Dv ( BIO_READ )
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are handled locally unless an I/O error occurs or the local version of the data
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is not up-to-date yet (synchronization is in progress).
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.Pp
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The
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.Nm
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daemon uses the GEOM Gate class to receive I/O requests from the
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in-kernel GEOM infrastructure.
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The
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.Nm geom_gate.ko
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module is loaded automatically if the kernel was not compiled with the
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following option:
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.Bd -ragged -offset indent
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.Cd "options GEOM_GATE"
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.Ed
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.Pp
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The connection between two
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.Nm
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daemons is always initiated from the one running as primary to the one
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running as secondary.
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When the primary
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.Nm
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is unable to connect or the connection fails, it will try to re-establish
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the connection every few seconds.
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Once the connection is established, the primary
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.Nm
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will synchronize every extent that was modified during connection outage
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to the secondary
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.Nm .
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.Pp
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It is possible that in the case of a connection outage between the nodes the
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.Nm
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primary role for the given resource will be configured on both nodes.
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This in turn leads to incompatible data modifications.
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Such a condition is called a split-brain and cannot be automatically
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resolved by the
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.Nm
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daemon as this will lead most likely to data corruption or loss of
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important changes.
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Even though it cannot be fixed by
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.Nm
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itself, it will be detected and a further connection between independently
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modified nodes will not be possible.
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Once this situation is manually resolved by an administrator, the resource
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on one of the nodes can be initialized (erasing local data), which makes
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a connection to the remote node possible again.
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Connection of the freshly initialized component will trigger full resource
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synchronization.
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.Pp
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A
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.Nm
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daemon never picks its role automatically.
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The role has to be configured with the
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.Xr hastctl 8
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control utility by additional software like
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.Nm ucarp
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or
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.Nm heartbeat
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that can reliably manage role separation and switch secondary node to
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primary role in case of the primary's failure.
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.Pp
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The
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.Nm
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daemon can be started with the following command line arguments:
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.Bl -tag -width ".Fl P Ar pidfile"
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.It Fl c Ar config
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Specify alternative location of the configuration file.
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The default location is
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.Pa /etc/hast.conf .
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.It Fl d
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Print or log debugging information.
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This option can be specified multiple times to raise the verbosity
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level.
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.It Fl F
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Start the
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.Nm
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daemon in the foreground.
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By default
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.Nm
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starts in the background.
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.It Fl h
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Print the
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.Nm
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usage message.
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.It Fl P Ar pidfile
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Specify alternative location of a file where main process PID will be
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stored.
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The default location is
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.Pa /var/run/hastd.pid .
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.El
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.Sh FILES
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.Bl -tag -width ".Pa /var/run/hastd.pid" -compact
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.It Pa /etc/hast.conf
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The configuration file for
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.Nm
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and
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.Xr hastctl 8 .
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.It Pa /var/run/hastctl
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Control socket used by the
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.Xr hastctl 8
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control utility to communicate with
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.Nm .
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.It Pa /var/run/hastd.pid
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The default location of the
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.Nm
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PID file.
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.El
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.Sh EXIT STATUS
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Exit status is 0 on success, or one of the values described in
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.Xr sysexits 3
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on failure.
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.Sh EXAMPLES
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Launch
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.Nm
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on both nodes.
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Set role for resource
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.Nm shared
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to primary on
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.Nm nodeA
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and to secondary on
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.Nm nodeB .
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Create file system on
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.Pa /dev/hast/shared
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provider and mount it.
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.Bd -literal -offset indent
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nodeB# hastd
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nodeB# hastctl role secondary shared
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nodeA# hastd
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nodeA# hastctl role primary shared
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nodeA# newfs -U /dev/hast/shared
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nodeA# mount -o noatime /dev/hast/shared /shared
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.Ed
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.Sh SEE ALSO
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.Xr sysexits 3 ,
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.Xr geom 4 ,
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.Xr hast.conf 5 ,
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.Xr ggatec 8 ,
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.Xr ggated 8 ,
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.Xr ggatel 8 ,
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.Xr hastctl 8 ,
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.Xr mount 8 ,
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.Xr newfs 8 ,
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.Xr g_bio 9
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.Sh AUTHORS
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The
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.Nm
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was developed by
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.An Pawel Jakub Dawidek Aq Mt pjd@FreeBSD.org
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under sponsorship of the FreeBSD Foundation.
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