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A <emphasis>striped plex</emphasis> stripes the data across each subdisk. The subdisks must all be the same size and there must be at least two subdisks in order to distinguish it from a concatenated plex. The greatest advantage of striped plexes is that they reduce hot spots. By choosing an optimum sized stripe, about 256 kB, the load can be evened out on the component drives. Extending a plex by adding new subdisks is so complicated that <filename>vinum</filename> does not implement it.
<xref linkend="vinum-comparison"/> summarizes the advantages and disadvantages of each plex organization.
<filename>vinum</filename> Plex Organizations
Plex type
Minimum subdisks
Can add subdisks
Must be equal size
Application
concatenated
1
yes
no
Large data storage with maximum placement flexibility and moderate performance
striped
2
High performance in combination with highly concurrent access
Some Examples
<filename>vinum</filename> maintains a <emphasis>configuration database</emphasis> which describes the objects known to an individual system. Initially, the user creates the configuration database from one or more configuration files using <citerefentry><refentrytitle>gvinum</refentrytitle><manvolnum>8</manvolnum></citerefentry>. <filename>vinum</filename> stores a copy of its configuration database on each disk <emphasis>device</emphasis> under its control. This database is updated on each state change, so that a restart accurately restores the state of each <filename>vinum</filename> object.
The Configuration File
The configuration file describes individual <filename>vinum</filename> objects. The definition of a simple volume might be:
drive a device /dev/da3h
volume myvol
plex org concat
sd length 512m drive a
This file describes four <filename>vinum</filename> objects:
The <emphasis>drive</emphasis> line describes a disk partition (<emphasis>drive</emphasis>) and its location relative to the underlying hardware. It is given the symbolic name <emphasis>a</emphasis>. This separation of symbolic names from device names allows disks to be moved from one location to another without confusion.
The <emphasis>volume</emphasis> line describes a volume. The only required attribute is the name, in this case <emphasis>myvol</emphasis>.
The <emphasis>plex</emphasis> line defines a plex. The only required parameter is the organization, in this case <emphasis>concat</emphasis>. No name is necessary as the system automatically generates a name from the volume name by adding the suffix <emphasis>.p</emphasis><emphasis>x</emphasis>, where <emphasis>x</emphasis> is the number of the plex in the volume. Thus this plex will be called <emphasis>myvol.p0</emphasis>.
The <emphasis>sd</emphasis> line describes a subdisk. The minimum specifications are the name of a drive on which to store it, and the length of the subdisk. No name is necessary as the system automatically assigns names derived from the plex name by adding the suffix <emphasis>.s</emphasis><emphasis>x</emphasis>, where <emphasis>x</emphasis> is the number of the subdisk in the plex. Thus <filename>vinum</filename> gives this subdisk the name <emphasis>myvol.p0.s0</emphasis>.
After processing this file, <citerefentry><refentrytitle>gvinum</refentrytitle><manvolnum>8</manvolnum></citerefentry> produces the following output:

<prompt>#</prompt> gvinum -&gt; <userinput>create config1</userinput>
Configuration summary
Drives: 1 (4 configured)
Volumes: 1 (4 configured)
Plexes: 1 (8 configured)
Subdisks: 1 (16 configured)

D a State: up Device /dev/da3h Avail: 2061/2573 MB (80%)

V myvol State: up Plexes: 1 Size: 512 MB

P myvol.p0 C State: up Subdisks: 1 Size: 512 MB

S myvol.p0.s0 State: up PO: 0 B Size: 512 MB
This output shows the brief listing format of <citerefentry><refentrytitle>gvinum</refentrytitle><manvolnum>8</manvolnum></citerefentry>. It is represented graphically in <xref linkend="vinum-simple-vol"/>.
A Simple <filename>vinum</filename> Volume
_ external ref='vinum-simple-vol' md5='__failed__'

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Source information

Source string comment
(itstool) path: row/entry
Flags
read-only
Source string location
article.translate.xml:428
String age
a year ago
Source string age
a year ago
Translation file
articles/vinum.pot, string 72