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nsr_storage_node - description of the storage node feature


       The storage node feature provides central server control of distributed
       devices for saving and recovering client data.


       A storage node is a host that has directly attached  devices  that  are
       used  and  controlled by a NetWorker server.   These devices are called
       remote devices, because they are remote from the server.   Clients  may
       save  and  recover  to  these remote devices by altering their "storage
       nodes" attribute (see nsr_client(5)).  A storage node  may  also  be  a
       client of the server, and may save to its own devices.

       The  main  advantages  provided  by this feature are central control of
       remote devices, reduction of network traffic, use of faster local saves
       and recovers on a storage node, and support of heterogeneous server and
       storage node architectures.

       There are several attributes which affect this  function.   Within  the
       NSR  resource (see nsr_service(5)) there are the "nsrmmd polling inter-
       val",  "nsrmmd  restart  interval"   and   "nsrmmd   control   timeout"
       attributes.   These  attributes control how often the remote media dae-
       mons (see nsrmmd(1)) are polled, how long between restart attempts, and
       how long to wait for remote requests to complete.

       Within  the  "NSR  device"  resource (see nsr_device(5)) the resource's
       name will accept the  "rd=hostname:dev_path"  format  when  defining  a
       remote  device.  The "hostname" is the hostname of the storage node and
       "dev_path" is the device path of the  device  attached  to  that  host.
       There  are also hidden attributes called "save mount timeout" and "save
       lockout," which allow a pending save mount request to  timeout,  and  a
       storage node to be locked out for upcoming save requests.

       Within  the "NSR client" resource (see nsr_client(5)), there are "stor-
       age nodes" and "clone storage nodes" attributes.  The  "storage  nodes"
       attribute  is  used  by the server in selecting a storage node when the
       client is saving data.  The "clone storage  nodes"  attribute  is  used
       during cloning, to direct cloned data from a volume on the storage node
       (the node represented by this client resource).

       The "NSR jukebox" resource (see  nsr_jukebox(5)),  contains  the  "read
       hostname"  attribute.  When all of a jukebox's devices are not attached
       to the same host, this attribute specifies the hostname that is used in
       selecting a storage node for recover and read-side clone requests.  For
       recover requests, if the  required  volume  is  not  mounted,  and  the
       client's  "storage  nodes"  attribute  does not match one of the owning
       hosts in the jukebox, then this attribute is used.  For clone requests,
       if the required volume is not mounted, then this attribute is used.


       In  order to install a storage node, choose the client and storage node
       packages, where given the choice.  For those platforms that do not have
       a choice, the storage node binaries are included in the client package.
       after adding root@storage_node  to  the  server's  administrator  list,
       (where  root  is  the  user running jbconfig(1) and storage_node is the
       hostname of the storage node).  This administrator list  entry  may  be
       removed after jbconfig(1) completes.

       In  addition to jbconfig(1), when running scanner(1) on a storage node,
       root@storage_node must be on the adminstrator list.

       When a device is defined (or enabled) on a  storage  node,  the  server
       will  attempt  to start a media daemon (see nsrmmd(1)) on the node.  In
       order for the server to know whether the node is alive,  it  polls  the
       node  every "nsrmmd polling interval" minutes.  When the server detects
       a problem with the node's daemon or the node  itself,  it  attempts  to
       restart  the  daemon  every  "nsrmmd  restart  interval" minutes, until
       either the daemon is restarted or the device is  disabled  (by  setting
       "enabled" to "no" in the device's "enabled" attribute).

       In  addition  to  needing a storage node enabler for each storage node,
       each jukebox will need its own jukebox enabler.


       A storage node is assignable for work when it is considered  functional
       by the server - nsrexecd(1) running, device enabled, nsrmmd(1) running,
       and the node is responding to the server's polls.  When a  client  save
       starts,  the  client's  "storage  nodes"  attribute is used to select a
       storage node.  This attribute is a  list  of  storage  node  hostnames,
       which are considered in order, for assignment to the request.

       The  exception  to  this  node assignment approach is when the server's
       index or bootstrap is being saved - these save sets are always directed
       to  the  server's  local  devices,  regardless of the server's "storage
       nodes" attribute.  Hence, the server will always need a local device to
       backup such data, at a minimum.  These save sets can later be cloned to
       a storage node, as can any save set.

       If a storage node is created first (by defining a device on the  host),
       and  a  client  resource  for that host is then added, that hostname is
       added to its "storage nodes" attribute.  This addition means the client
       will back up to its own devices.  However, if a client resource already
       exists, and a device is later defined on that host, then  the  client's
       hostname  must  be  added  manually  to  the  client's  "storage nodes"
       attribute.  This attribute is an ordered list  of  hostnames;  add  the
       client's own name as the first entry.

       The  volume's  location field is used to determine the host location of
       an unmounted volume.  The server looks for a device or jukebox name  in
       this field, as would be added when a volume resides in a jukebox.  Vol-
       umes in a jukebox are considered to be located on the host to which the
       jukebox  is connected.  The location field can be used to bind a stand-
       alone volume to a particular node by manually setting this field to any
       device  on  that node (using the "rd=" syntax).  For jukeboxes which do
       not have all of their devices attached to the same host, see the previ-
       ous description of the "read hostname" attribute.

       There are several commands that interact directly with a device, and so
       must run on a storage node.  These include  jbconfig(1),  nsrjb(1)  and
       scanner(1),  in addition to those in the device driver package.  Invoke
       these commands directly on the storage node rather than on the  server,
       respectively.  Such a request would be divided into  two  sub-requests,
       one  to  read  volumeA  from storage node A and another to read volumeB
       from storage node B.

       A clone request involves two sides, the source that reads data and  the
       target that writes data.  These two sides may be on the same host or on
       different hosts, depending on the configuration.  The  source  host  is
       determined  first  and then the target host.  If the volume is mounted,
       the source host is determined by its current mount  location.   If  the
       volume  is  not mounted at the time of the clone request and it resides
       in a jukebox, then the source host is determined by the  value  of  the
       jukebox's "read hostname" attribute.

       Once the source host is known, the target host is determined by examin-
       ing the "clone storage nodes" attribute of the client resource  of  the
       source host.  If this attribute has no value, the "clone storage nodes"
       attribute of the  server's  client  resource  is  consulted.   If  this
       attribute  has  no value, the "storage nodes" attribute of the server's
       client resource is used.


       A server cannot be a storage node of another server.


       jbconfig(1), mmlocate(1), nsr_client(5), nsr_device(5), nsr_jukebox(5),
       nsr_service(5),  nsrclone(1),  nsrexecd(1),  nsrjb(1),  nsrmmd(1), 
       nsrmon(1), scanner(1).


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