Disk arrays are groups of disks that work together with a specialized array controller to take advantage of potentially higher data transfer rates and, depending on the RAID level selected, data redundancy.
Disk arrays use RAID technology to offer data redundancy and improved data transfer rates over those provided by single large disks. If a disk failure occurs, the disk can usually be replaced without interrupting normal system operation.
Data redundancy
The disk array controller keeps track of how the data is distributed across the disks. RAID 5, 6, and 10 disk arrays also provide data redundancy, so that no data is lost if a single disk in the array fails. If a disk failure occurs, the disk can usually be replaced without interrupting normal system operation.
Using arrays
Each disk array can be used by AIX® in the same way as it would a single non-RAID disk. For example, after creating a disk array, you can create a file system on the disk array or use AIX commands to make the disk array available to the system by adding the disk array to a volume group.
hdisk
Like other disk storage units in AIX, the disk arrays are assigned names using the hdisk form. The names are deleted when you delete the disk array. An hdisk is a disk that is formatted to 512 bytes per sector. These disks must be formatted to 528 bytes per sector before they can be used in disk arrays.
pdisk
The individual physical disks that comprise disk arrays (or serve as candidates to be used in disk arrays) are represented by pdisk names. A pdisk is a disk that is formatted to 528 bytes per sector.
Array management
The IBM® SAS RAID controller is managed by the IBM SAS Disk Array Manager. The disk array manager serves as the interface to the controller and I/O device configuration. It is also responsible for the monitoring and recovery features of the controller.
Boot device
If a disk array is to be used as the boot device, you might have to prepare the disks by booting from the IBM server hardware stand-alone diagnostics CD and creating the disk array before installing AIX. You might want to perform this procedure when the original boot drive is to be used as part of a disk array.
Array configuration
The List SAS Disk Array Configuration option in the disk array manager can be used to display the pdisk and hdisk names, their associated location codes, and their current state of operation. The following sample output is displayed when the List SAS Disk Array Configuration option is invoked.
+--------------------------------------------------------------------------------+ | | | ------------------------------------------------------------------------ | | Name Resource State Description Size | | ------------------------------------------------------------------------ | | sissas0 FFFFFFFF Primary PCI-X266 Planar 3 Gb SAS Adapter | | | | hdisk8 00FF0100 Optimal RAID 6 Array 69.6GB | | pdisk0 00040100 Active Array Member 34.8GB | | pdisk2 00040B00 Active Array Member 34.8GB | | pdisk8 00000500 Active Array Member 34.8GB | | pdisk9 00000A00 Active Array Member 34.8GB | | | | hdisk7 00FF0000 Optimal RAID 0 Array 34.8GB | | pdisk4 00040000 Active Array Member 34.8GB | | | | hdisk13 00FF0300 Optimal RAID 0 Array 34.8GB | | pdisk5 00040300 Active Array Member 34.8GB | | | | hdisk14 00FF0400 Failed RAID 0 Array 34.8GB | | pdisk3 00040A00 Failed Array Member 34.8GB | | | | hdisk0 00040500 Available SAS Disk Drive 146.8GB | | hdisk1 00040600 Available SAS Disk Drive 146.8GB | | hdisk3 00000600 Available SAS Disk Drive 73.4GB | | | | | +--------------------------------------------------------------------------------+
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