97 lines
6.4 KiB
HTML
97 lines
6.4 KiB
HTML
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<meta name="dc.date" scheme="iso8601" content="2005-09-13" />
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<meta name="copyright" content="(C) Copyright IBM Corporation 1998, 2006" />
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<title>i5/OS storage management</title>
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<a name="rzahqstormgtconcept"></a>
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<h2 id="rzahqstormgtconcept">i5/OS storage management</h2>
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<p>This brief overview of i5/OS™ storage management concepts is intended
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for administrators who are more familiar with how Windows servers manage storage.
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Because i5/OS handles storage management differently than a PC server, some techniques
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that you need in the PC server world are unnecessary in the Windows environment
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on iSeries™.</p>
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<p><span class="bold">i5/OS and disk drives</span></p>
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<p>i5/OS, the operating system that runs on an iSeries, does not need to deal directly with
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disk drives. Beneath the operating system a level of software (called System
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Licensed Internal Code (SLIC)) "hides" the disk drives and manages the storage
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of objects on those disk drives. A virtual address space is mapped over the
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existing disk space and used for addressing objects rather than disk drive
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IDs, cylinders, and sectors. Needed objects are copied ("paged in") from this
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address space on disk into the address space of main memory.</p>
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<p>Because of the way i5/OS manages disk data, you do not generally need to worry
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about partitioning high-growth databases, defragmenting disks, or disk striping
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on your integrated server. The integrated server uses device drivers to share
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the i5/OS disk drives. These device drivers send and receive disk data to
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the i5/OS storage management subsystem. i5/OS storage management handles the hard disks,
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including spreading the Windows disk drive images across multiple hard disk
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drives and applying RAID and file mirroring (if configured). Disk defragmentation
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software manages logical file fragmentation of the hard disk images. Because i5/OS storage management handles these tasks, running a defragmentation program
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on the integrated server helps primarily in cases where in cases where "critical
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file system structures" can be defragmented.</p>
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<p><span class="bold">Disk pools (ASPs)</span></p>
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<p>In i5/OS physical hard disk drives are pooled together into one storage
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space called a disk pool, also called an auxiliary storage pool (ASP). If
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your file system runs out of space, you can add a new hard disk drive to the
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disk pool, and the new storage space will be available immediately. Every
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system has at least one disk pool, the system disk pool. The system disk pool
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is always ASP 1. You can configure additional <span class="italic">user</span> disk
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pools, numbered 2 - 255. You can use disk pools to distribute your i5/OS data over different
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groups of disks. You can also use this concept to move less important applications
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or data to your older, slower disk drives. Support for independent ASPs (33-255)
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is provided through iSeries Navigator. Both the Information Center and iSeries Navigator refer to ASPs as Disk Pools.</p>
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<p><span class="bold">Disk protection:</span></p>
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<p>i5/OS disks can be protected in two ways:</p>
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<ul>
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<li><img src="delta.gif" alt="Start of change" /><span class="bold">Cross-site mirroring</span>
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<br />Cross-site
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mirroring, using the operating system geographic mirroring function for IASPs,
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mirrors data on disks at sites that can be separated by a significant distance.<img src="deltaend.gif" alt="End of change" /></li>
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<li><span class="bold">RAID-5</span>
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<br />The RAID-5 technique
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groups several disks together to form an array. Each disk holds checksum information
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of the other disks in the same array. If a disk fails, the RAID-5 disk controller
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can re-create the data of the failing disk with the help of the checksum information
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about the other disks. When you replace a failing disk with a new one, i5/OS can rebuild the information from the failed disk on the new (and therefore
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empty) disk.</li>
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<li><span class="bold">Mirroring</span>
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<br />Mirroring keeps
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two copies of data on two different disks. i5/OS performs write operations on both disks
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at the same time, and can simultaneously perform two different read operations
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on the two disks of a mirrored pair. If one disk fails, i5/OS uses information
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from the second disk. When you replace the failing disk, i5/OS copies the
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data from the intact disk to the new disk.</li></ul>
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<p>To further increase the level of protection, you can attach the mirrored
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disks to two different disk controllers. Then if one controller fails, and
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with it one set of disks, the other controller can keep the system up. On
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larger models of iSeries, you can attach controllers to more than one bus.
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Attaching the two disk controllers that form a mirrored pair to two different
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buses increases availability even more.</p>
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<p>You can define disk pools on i5/OS to have different levels of protection
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or no protection at all. Then you can put applications and data into a disk
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pool with the right amount of protection, depending on how important their
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availability is. For more information about i5/OS disk protection and availability options,
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read <a href="../books/sc415304.pdf" target="_blank">Backup and Recovery</a>.</p>
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