Dell PowerVault MD3260i CLI Guide - Page 108

You do not need to enter a value for the cacheReadPrefetch parameter or the segmentSize parameter. If you do not enter a value, the RAID controller module firmware uses the usageHint parameter with fileSystem as the default value. Entering a value for the usageHint parameter and a value for the cacheReadPrefetch parameter or a value for the segmentSize parameter does not cause an error. The value that you enter for the cacheReadPrefetch parameter or the segmentSize parameter takes priority over the value for the usageHint parameter. Segment Size The size of a segment determines how many data blocks that the RAID controller module writes on a single physical disk in a virtual disk before writing data on the next physical disk. Each data block stores 512 bytes of data. A data block is the smallest unit of storage. The size of a segment determines how many data blocks that it contains. For example, an 8 KB segment holds 16 data blocks. A 64 KB segment holds 128 data blocks. When you enter a value for the segment size, the value is checked against the supported values that are provided by the RAID controller module at run time. If the value that you entered is not valid, the RAID controller module returns a list of valid values. Using a single physical disk for a single request leaves other physical disks available to simultaneously service other requests. If the virtual disk is in an environment where a single user is transferring large units of data (such as multimedia), performance is maximized when a single data transfer request is serviced with a single data stripe. A data stripe is the segment size that is multiplied by the number of physical disks in the disk group that are used for data transfers. In this case, multiple physical disks are used for the same request, but each physical disk is accessed only once. For optimal performance in a multiuser database or file system storage environment, set your segment size to minimize the number of physical disks that are required to satisfy a data transfer request. Security Type The securityType parameter is valid for physical disks that are capable of selfencrypting disk (SED). With SED, the RAID controller module firmware can create a key and activate the physical disk security feature. The physical disk security feature encrypts data as the data is written to the physical disk and decrypts the data as the data is read from the physical disk. Without the key created by the RAID controller module, the data written to the physical disk is inaccessible. Before you can set the securityType parameter to capable or enabled, you must create a storage array security key. Use the create storageArray securityKey command to create a storage array security key. The following commands are related to the security key: • create storageArray securityKey • set storageArray securityKey • start secureErase (physicalDisk | physicalDisks) • enable diskGroup [diskGroupName] security Enclosure Loss Protection and Drawer Loss Protection For enclosure loss protection to work, each physical disk in a disk group must be in a separate enclosure. If you set the enclosureLossProtect parameter to TRUE and have selected more than one physical disk from any one enclosure, the storage array returns an error. If you set the enclosureLossProtect parameter to FALSE, the storage array performs operations, but the disk group that you create might not have enclosure loss protection. Enclosure loss protection is not valid when you create virtual disks on existing disk groups. The drawerLossProtect parameter defines if data on a virtual disk is accessible if a drawer fails. When you assign the physical disks, if you set the drawerLossProtect parameter to TRUE and select more than one physical disk from any one drawer, the storage array returns an error. If you set the drawerLossProtect parameter to FALSE, the storage array performs operations, but the disk group that you create might not have drawer loss protection. You must set the enclosureLossProtect parameter and the drawerLossProtect parameter to the same value. Either both the parameters must be TRUE or both must be FALSE. If the enclosureLossProtect parameter and the drawerLossProtect parameter are set to different values, the storage array returns an error. 108