HP P3410A HP NetRAID 1M/2M Installation & Configuration - Page 89

Chapter 7 Preparing for Online Capacity Expansion For example, assume you have one RAID-5 logical drive built from four physical hard disk drives of 4 GB each. The result is 12 GB of actual storage space. If you enable virtual sizing for this logical drive, then the operating system will see a logical drive of 144 GB. Only the first 12 GB are real, 4 GB are used for parity, and the last 128 GB are virtual. Under NetWare 4.2, you create a 144 GB partition, but within that partition you only create a logical drive totaling 12 GB or less. Since there is unused partition space, the physical storage of 12 GB can be expanded online by adding another hard disk drive, but the partition remains at 144 GB. To actually expand capacity online, refer to the HP NetRAID Series User Guide and your NetWare documentation. Precautions When using the Online Capacity Expansion feature, it is very important that you do not create volumes that exceed the actual physical capacity. You must add up the capacities of all volumes that may be using the physical storage space, such as a DOS volume, SYS volume, Hot Fix Area, and any user volumes. This is most important if NetWare 4.2 will be installed on the disk array (rather than a SCSI disk outside of the HP NetRAID system). During installation, if the total physical capacity is exceeded during volume creation, a NetWare abend and loss of the installation occurs. As long as the physical capacity is not exceeded, the installation will be successful. Although undesirable, NetWare 4.2 allows you to create volumes into the virtual space. (This is because during volume creation, NetWare 4.2 only looks at the beginning of the volume and if there is real storage space there, the volume will be created.) However, when writing to this volume, you cannot write beyond the physical limit and write errors will be generated when the physical space is filled. You need to be careful when creating volumes in a partition containing virtual space. Use the HP NetRAID Config module to check the actual physical capacity available, and be sure the total size of NetWare volumes does not exceed this value. One other useful measure is to set the capacity alarms under NetWare 4.2 so that warnings will be generated when you approach the limit of a volume. The Online Capacity Expansion feature cannot be used if a logical drive spans multiple arrays. Each array can contain only one logical drive. Reconstruction (for the purposes of adding a drive to an array) can be done only on an array having a single logical drive. It is also important to plan future storage expansion into your installation. This ensures that you can easily expand capacity without the need for backup/restore operations or reconfiguration. 81