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<h1 class="topictitle1">Dynamically adding disks to a Linux partition</h1>
<div><p>Virtual devices simplify hardware configuration on the iSeries™ server
because they do not require you to add additional physical devices to the
server in order to run Linux. </p>
<div class="p">You can allocate up to 64 virtual disks to a Linux partition, with
a maximum of twenty disks visible to Linux, depending on which distribution
you use. Each disk supports up to 1000 GB of storage. Each virtual disk appears
to Linux as a single physical unit. However, the associated space in the i5/OS<sup>®</sup> integrated
file system is spread across all of the disk arms available on the iSeries server.
This provides the benefits of RAID without the overhead of RAID support in
the Linux kernel.<p>i5/OS provides the ability to dynamically add virtual
disks to a Linux partition. You can allocate disk space in the integrated
files system and make it available to Linux without restarting i5/OS or Linux.
The Linux server administrator can also configure the newly allocated disk
space and make it available, again without interrupting the server.</p>
</div>
<div class="section">To dynamically add virtual disks to a Linux partition, do the following:</div>
<ol><li class="stepexpand"><span>Create a disk drive using iSeries Navigator.</span><ol type="a"><li><span>Click <span class="menucascade"><span class="uicontrol">Network</span> &gt; <span class="uicontrol">Windows
Administration</span></span>.</span></li>
<li><span>Right-click the <span class="uicontrol">Disk Drives</span> folder and
click <span class="uicontrol">New Disk</span>.</span></li>
<li><span>In the Disk drive name field, specify a disk drive name.</span></li>
<li><span>In the Description field, specify a description of this disk.</span></li>
<li><span>If you want to copy data from another disk, select <span class="uicontrol">Initialize
disk with data from another disk</span>. Then specify the source disk
to copy data from.</span></li>
<li><span>In the Capacity field, specify the disk capacity.</span></li>
<li><span>Click <span class="uicontrol">OK</span>.</span></li>
</ol>
</li>
<li class="stepexpand"><span>Link a disk drive using iSeries Navigator.</span><ol type="a"><li><span>Click <span class="menucascade"><span class="uicontrol">Network</span> &gt; <span class="uicontrol">Windows
Administration</span> &gt; <span class="uicontrol">Disk Drives</span></span>.</span></li>
<li><span>Right-click an available disk drive and select <span class="uicontrol">Add
Link</span>.</span></li>
<li><span>Select the server that you want to link the disk to.</span></li>
<li><span>Select one of the available link types and the link sequence
position.</span></li>
<li><span>Select one of the available data access types.</span></li>
<li><span>Click <span class="uicontrol">OK</span>.</span></li>
</ol>
</li>
<li class="stepexpand"><span>Determine the device name of the new disk. </span> As far as i5/OS is
concerned, the space is available to the Linux partition. Now you need to
run through a couple of steps within Linux to partition, format, and access
the disk. The name depends on two factors:<ul><li>The distribution of Linux</li>
<li>The number of disks currently allocated</li>
</ul>
<p> For example, with the SUSE distribution with a single disk allocated,
the first disk device is known as <kbd class="userinput">/dev/hda</kbd>. The second
disk (the newly allocated virtual disk) is known as <kbd class="userinput">/dev/hdb</kbd>.</p>
</li>
<li class="stepexpand"><span>Create partitions on the new disk with the fdisk command in Linux.</span> The fdisk command is a standard Linux command and is the same for all
distributions. You must have superuser (also known as <dfn class="term">root</dfn>) privileges
to execute this command.<ol type="a"><li><span>From the command line, type <kbd class="userinput">fdisk /dev/hdb</kbd> and
press <span class="uicontrol">Enter</span>.</span></li>
</ol>
The command responds with the following prompt: <tt class="sysout">Command
(m for help):</tt></li>
<li class="stepexpand"><span>Type <span class="uicontrol">p</span> (for print) at the prompt to display
the current partition table for the disk. </span> By default, a new virtual
disk shows a single partition formatted as FAT16. For example, <pre>Disk /dev/hdb: 64 heads, 32 sectors, 200 cylinders
Units = cylinders of 2048 * 512 bytes
Device Boot Start End Blocks Id System
/dev/hdb1 1 199 203760 6 FAT16</pre>
</li>
<li class="stepexpand"><span>Delete the partition.</span> The FAT16 partition is not required.
You need to delete the current partition and then create a new one. <ol type="a"><li><span>To delete the partition, Type <span class="uicontrol">d</span> at the
command prompt.</span></li>
</ol>
The fdisk command responds with the following prompt: <tt class="sysout">Partition
number (1-4):</tt></li>
<li class="stepexpand"><span>Enter the partition number (in this case, 1), and press <span class="uicontrol">Enter</span>. </span> The fdisk prompt returns a message indicating that the deletion was
successful.</li>
<li class="stepexpand"><span>Create a new partition.</span><ol type="a"><li class="substepexpand"><span>Type the command <span class="uicontrol">n</span> for a new partition.</span> The fdisk prompt returns the following:<pre>Command action
E extended
P primary partition (1-4)</pre>
</li>
<li class="substepexpand"><span>Type the command <span class="uicontrol">p</span> and press <span class="uicontrol">Enter</span>.</span> The fdisk prompt returns the following:<pre>Partition number (1-4):</pre>
</li>
<li class="substepexpand"><span>Since this is the first partition on the disk, enter <span class="uicontrol">1</span> and
press <span class="uicontrol">Enter</span>. </span> The fdisk prompt returns the
following:<pre>First cylinder (1-200, default 1):</pre>
</li>
<li class="substepexpand"><span>Type <span class="uicontrol">1</span> and press <span class="uicontrol">Enter</span>. </span> The fdisk prompt returns the following:<pre>Last cylinder or +size or +sizeM or +sizeK (1-200, default 200):</pre>
</li>
<li class="substepexpand"><span>Type <span class="uicontrol">200</span> and press <span class="uicontrol">Enter</span>. </span> The fdisk prompt appears again, indicating that the partition
creation was successful.<div class="note"><span class="notetitle">Note:</span> The type of the partition defaults to Linux.
If you need a different disk type (like LVM, or Linux Extended), use the <span class="uicontrol">t</span> (for
type) command to change the type of the partition.</div>
</li>
</ol>
</li>
<li class="stepexpand"><span>Type w (for write) to commit the changes and press <span class="uicontrol">Enter</span>.</span> Up until this point, you have made no changes to the disk structure.
After you commit the changes, fdisk responds with the following diagnostic
messages: <pre>The partition table has been altered!
Calling ioctl() to re-read partition table.
Syncing disks.</pre>
</li>
<li class="stepexpand"><span>Type <kbd class="userinput">mkfs</kbd> to format the new partition. </span> The mkfs command is a standard Linux command that should be available
on each Linux distribution. There are a number of optional parameters for
mkfs, but typically the defaults satisfy most disk uses. To format the partition
created in the previous steps, enter the following command (again, as with
the fdisk command, you need to be logged in as root to execute the mkfs command):<pre>mkfs /dev/hdb1</pre>
<p>Remember
that a single partition exists on the second disk. Hence the name /dev/hdb1
(the hdb indicates that it is the second disk, and the 1 indicates that it
is partition 1). The following diagnostic messages appear:</p>
<pre>mke2fs 1.28 (31-Aug-2002)
Fileserver label=
OS type: Linux
Block size=1024 (log=0)
Fragment size=1024 (log=0)
51200 inodes, 204784 blocks
10239 blocks (5.00%) reserved for the super user
First data block=1
25 block groups
8192 blocks per group, 8192 fragments per group
2048 inodes per group
Superblock backkups stored on blocks:
8193, 24577, 40961, 57345, 73729
Writing inode tables: done
Writing superblocks and fileserver accounting information: done
This fileserver will be automatically checked every 29 mounts or
180 days, whichever comes first. Use tune2fs -c or -i to override.</pre>
</li>
<li class="stepexpand"><span>Create a new directory. </span> Finally, within the Linux file
tree, you need to create a directory that you can use to access the new file
system. You also need to allocate the new fileserver to that point within
the directory tree. To do this, we create a directory and mount the physical
resource as follows:<ol type="a"><li><span>Type <kbd class="userinput">mkdir /mnt/data</kbd> and press <span class="uicontrol">Enter</span>.</span></li>
<li><span>Type <kbd class="userinput">mount /dev/hdb1 /mnt/data</kbd> and press <span class="uicontrol">Enter</span>.</span></li>
</ol>
</li>
<li class="stepexpand"><span>Add an entry. </span> You now have new virtual disk space available
to the running Linux partition. To facilitate automatic mounting of the resource
across Linux starts, add an entry to the <samp class="codeph">/etc/fstab</samp> file
(this is the file that stores mount definitions). For this example, the entry
in <samp class="codeph">/etc/fstab</samp> would appear as follows:<pre>/dev/hdb1 /mnt/data ext2 defaults 1 1</pre>
</li>
</ol>
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