Adaptec 2074700-R User Guide - Page 141
Notes on the Configuration of RAID 0, 1, 4, 5 and 10 Arrays Drives
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ICP RAID Console 10.5.4.3 Notes on the Configuration of RAID 0, 1, 4, 5 and 10 Arrays Drives Use logical drives of the type disk to build an array drive. RAID array drives can be configured with logical drives of the type chain also, but security should be taken into consideration. For regular RAID array drives, type disk logical drives are used. Logical drives of an array drive should have the same storage capacity. To avoid wasting valuable storage capacity, use only logical drives that have the same storage capacity as the logical drive being replaced on that array. A hot fix drive provides the most security. One of the reasons RAID array drives are used, lies with the data redundancy they provide, that is, the data security you have in the event of a hard disk failure. For the purpose of the following considerations, we define the term time without redundancy (TWR) as the time it takes to replace a failed hard drive (assuming there is no hot fix drive installed in the system). The time without redundancy should be kept as short as possible, not including the time needed to set up the array drive (state build). Assume that one of the hard disks of a RAID 5 array drive has failed. The array drive is without redundancy. TWR begins. Any superfluous prolongation of the TWR (because you have to get a replacement hard disk, or because no one checked the file server) increases the risk of data loss should a second hard disk fail. Therefore, new redundancy should be created as soon as possible and in an entirely automated manner. Integrate a hot fix drive as an immediately available and auto-replacing hard disk to keep the TWR as short as possible. Only a hot fix drive can ensure optimal array drive security and constant data availability. Of course a hot fix drive is not mandatory. If you control the array drive at regular intervals and immediately replace a defective hard disk (by shutting down the system or using a hot fix), you can minimize the risk of data loss. 10.5.5 Configure Host Drives The Configure Host Drives option (Figure 10-104) allows you to configure host drives (level of hierarchy 4). These are the drives the host computer is aware of. Host drives can consist of a single hard disk, or of many hard disks built to create a RAID 5 array drive. This menu option is similar to the Configure Host Drives option in Express Setup (see Section 10.4.1). Unlike Express Setup, Advanced Setup allows the user to select a stripe size while Express Setup defaults the stripe size to 128KB. Also, Advanced Setup has the Split Host Drive, Merge Host Drives, and Partition Drive menu options. The additional capacity resulting from an online capacity expansion is shown as another host drive. If you expand the capacity of the array drive a second time, there would be three host drives belonging to the same array drive. Since there is currently no operating system which supports "growing hard disks", this expansion method is the only safe way to introduce new capacity. Software Installation and User's Guide 141