Dataless Management Services (DMS) lets client systems share the
/usr
file system on a centrally administered server over a network
while still maintaining their own root ( / )
and
/var
file systems that reside on the DMS server.
With
DMS, you can save disk space by sharing the actual operating system software
between systems.
A DMS server stores the operating system software in a DMS
area.
DMS clients access the operating system software across the local area
network (LAN) instead of from their local disks.
Without DMS, each system
maintains a copy of its operating system software on its own local hard disk.
Caution
DMS is not supported in a clusters environment.
This chapter includes the following topics:
Defining the DMS environment (Section 9.1)
Listing the benefits of DMS (Section 9.2)
Explaining the relationship between DMS servers and clients (Section 9.3)
In a Dataless Management Services (DMS) environment, a server system
maintains the root,
/usr, and
/var
file
systems for all client systems.
The server maintains one copy of the root
file system for each client.
The
/usr
file system is exported
read only and is shared by all clients registered to the environment.
Client
systems have their own
/var
file system.
All swapping and
dumping is done on the client's local disk.
The dataless management utility (dmu) creates a
root file system based on the software subsets installed in the DMS environment
area on the server.
This root file system is accessed by client systems over
a local area network (LAN).
DMS lets system administrators customize the root
and
/usr
file systems before client systems access them.
You must have superuser privileges to perform many of the
dmu
functions.
9.2 DMS Benefits
The advantages of installing DMS include the following:
Less disk space is required on client systems.
By sharing
the
/usr
area, you eliminate the need for disk space to
hold a separate
/usr
area for each client.
For Alpha systems,
you can save more than 425 megabytes (Mb) for each client.
Installation and setup of servers and clients are done by automated scripts, thereby simplifying the task of the server system administrator. Maintenance of the DMS areas is similarly straightforward.
Because the DMS files reside on the server, the server's system administrator can perform most system management tasks. The involvement of individual users with the complexities of system management is reduced.
9.3 Relationship Between DMS Servers and Clients
The DMS utility,
dmu, manages the sharing of installed
operating system software between servers and clients in a LAN.
In addition
to the server's normal disk area, one or more disk partitions are reserved
as the DMS area, made up of one or more product environments and client areas.
This section includes the following topics:
Describing the DMS server (Section 9.3.1)
Explaining the environment portion of a DMS area (Section 9.3.2)
Explaining the client portion of a DMS area (Section 9.3.3)
Describing DMS client characteristics (Section 9.3.4)
The DMS server maintains multiple copies of the root area, one for each
client.
Each copy is in a client root directory in the DMS area and is customized
for the client in order to provide for differences between hardware platforms
or environmental requirements.
Each of the client root directories is private;
this means that there is a directory for each client so that no conflict or
confusion exists between clients.
The server's DMS root and
/usr
areas are made available to clients by means of the Network File
System (NFS).
For more information about the NFS used by the operating system,
refer to the
Network Administration
guide.
Beyond verifying clients' identities, vectoring their boot requests, and providing their system disk space, the server does not interact directly with the clients. The server can support local timesharing users and need not be dedicated to DMS.
A DMS client's system disk space (root and
/usr
areas)
is physically connected to the server instead of to the client.
The client
accesses that disk area through a LAN connection with the server.
Each DMS
client is booted across the network from its private root area on the server.
Once booted, the client continues to use its root files and
/usr
files from the server's DMS area.
These files appear to the client
as if they were on local disks, as shown in
Figure 9-1.
Figure 9-1: File Sharing Between the DMS Server and Client
As indicated in
Figure 9-1, clients must have
local disks.
In addition to local disks, clients can import file systems
from any other computer to which they have network access.
Clients use swap
and dump space on their local disks.
9.3.2 Environment Portion of DMS Area
One or more
DMS environments
can
reside in a partition.
If you want to prevent the
dmu
utility
from putting all DMS environments in the same disk partition, indicate a unique
mount point for each DMS environment.
The DMS environment disk space requirements
should be calculated using the worksheets in
Appendix B.
Then the mount point of
./dmsn.alpha
should be added to
the
/etc/fstab
file.
Each DMS environment contains a customized directory and file system,
consisting of root,
/usr, and
/var.
The
dmu
utility copies the root area to the client area
when a client is added to the dataless environment.
Figure 9-2
shows the
/var/adm/dms
portion of a DMS area, it contains two DMS environments,
dms0.alpha
and
dms1.alpha.
Each DMS environment
contains a root and
/usr
file system.
The root file system
is copied to each client system.
The
/usr
file system is
read only and is shared among all client systems registered to the environment.
Figure 9-2: Environment Portion of DMS Area
The root file
system contains copies of the kernel,
.vmunix,
vmunix
and other primary system files.
These primary files can
be in either
new
form (files supplied
in the operating system distribution kit and prefixed with
.new..) or in
prototype
form (files
prefixed with
.proto..).
Do not customize the
.new..
version of a file.
The
.proto..
files have special significance for
DMS environments.
By modifying the
.proto..
files, you
can customize the DMS server to meet specific needs.
You can use these customized
.proto..
files when you configure the DMS client environments.
You
also can modify standard files such as
/etc/hosts
and
/etc/fstab
so that DMS clients do not have to modify them.
The
/usr
file system contains common files that can
be used without being tailored by clients registered to the DMS environment.
DMS environments
can be created with different combinations of products to allow servers to
provide diversified service based on client's software product needs.
For
example, you could have a DMS environment with only the base operating system.
Another DMS environment could have the base operating system plus any number
of additional products (such as DECLadebug or DEC Fortran) installed.
Multiple
environment areas can be established in separate partitions to support a variety
of environments, or to improve performance, or to support more clients than
allowed by the disk space available in the
/var/adm/dms
directory.
The server does not use any of the DMS area.
System administrators can
access the DMS area as required for maintenance and for installation or removal
of layered products, but the area is not used by the server itself.
9.3.3 Client Portion of DMS Area
A
DMS client area
for individual
DMS client systems also resides in a DMS area.
Figure 9-3
shows a DMS client area named
/clients.
Place this DMS
client area in its own partition after you calculate the required size with
the worksheets in
Appendix B.
Next, add the mount
point of the
/clients
DMS client area to the
/etc/fstab
file.
Figure 9-3: DMS Client Area
Multiple copies of the root
file system reside in the client area, one for each client, tailored from
the generic root file system.
Each client builds a customized kernel, which
resides in the client's root area if the client has a partial or full build
environment.
This customized kernel supports the client's actual system configuration,
including central processor, system memory, and peripheral devices.
Figure 9-3
shows two client root areas, named
ClientA
and
ClientB.
Each client sees its private
root area and the shared
/usr
area from the
/var/adm/dms
environment as local, although these areas are actually on the
DMS server and are accessed through NFS.
Figure 9-4
shows how clients share
/usr
and have their own root file
system.
You can establish multiple client areas but they must reside in different
partitions.
9.3.4 Characteristics of DMS Clients
Clients do not have access to the entire DMS area. Each DMS client has access to the root area assigned to it on the server.
Common system files residing in the
/usr
area are
shared among all the clients registered to that particular
/var/adm/dms
environment.
Mounted with read-only access for the clients, this
shared area is protected from erroneous client activity.
Figure 9-4
illustrates this concept.
Figure 9-4: Client Views of the DMS Area
In Figure 9-4, the small boxes represent what the clients think they see; the arrows show how the real disk areas on the server are mounted by the client to produce this view.
Clients can be timesharing systems or workstations. Because each client's root area is tailored specifically to the client's needs and would contain the software the client can run, there is no interference between clients attempting to use identical resources that could, for example, have licensing restrictions based on the number of concurrent users.