Disk arrays
RAID technology is used to store data across a group of disks known as a disk array.
Depending on the RAID level selected, the technique of storing data across a group of disks provides the data redundancy required to keep data secure and the system operational. If a disk failure occurs, the disk can usually be replaced without interrupting normal system operation. Disk arrays also have the potential to provide higher data transfer and input and output (I/O) rates than those provided by single large disks.
Each disk array can be used by Linux in the same way as it would a single SCSI disk. For example, after creating a disk array, you can use Linux commands to make the disk array available to the system by partitioning and creating file systems on it.
A tier is a grouping of physical disks within an Easy Tier® disk array all of which have the same performance characteristics. For example, an Easy Tier disk array may contain a tier of SSDs and a tier of HDDs. A data band is the block of data in an Easy Tier disk array that is being analyzed for I/O activity. This data band is the block of data that may move between tiers to better match the I/O activity within the band with the performance characteristics of the tier. The size of the data band can be 1 MB to 8 MB in size depending on the configuration of the Easy Tier disk array.
The SAS controller and I/O devices are managed by the iprconfig utility. The iprconfig utility is the interface to the RAID configuration, monitoring, and recovery features of the controller and I/O devices.
If a disk array is to be used as the boot device, it might be necessary to prepare the disks by booting into Rescue mode and creating the disk array before installing Linux. You might want to perform this procedure when the original boot drive is to be used as part of a disk array.
The following figure illustrates a possible disk array configuration.
Easy Tier function
Easy Tier function works with specific RAID levels (i.e., 5T2, 6T2, and 10T2) that support grouping disks with different performance characteristics but similar RAID block formats into tiers within a single array. The Easy Tier function automatically optimizes storage performance across the tiers by moving the physical data placement between the tiers while keeping the external disk view of the Disk array logical block locations unchanged. The Easy Tier function logically divides the Disk array into data bands and continually analyzes the I/O activity in each band. Based on the current I/O activity in each band, the Easy Tier function optimizes performance and resource utilization by automatically and non-disruptively swapping data bands between physical disk tiers containing the most appropriate performance characteristics for the current I/O activity in the band (for example, moving the hottest data to fastest tier.) The tiers are automatically organized such that the best performing tier aligns with disk array LBA 0 (the beginning of the array) when a new array is created before any of the data bands become swapped. It is important to note that a hot spare disk only replaces a disk in the tier that has the similar performance characteristics as the hot spare. Therefore, you need different hot spare disks to fully cover all tiers in a tiered RAID level. For example, an SSD hot spare and a HDD hot spare.- SSDs that have a high write endurance
- Read Intensive (RI) SSDs that are intended to be used for read-intensive workloads
- HDDs or Enterprise Nearline (ENL) HDDs
- SSDs and HDDs
- RI SSDs and HDDs
- SSDs and ENL HDDs
- RI SSDs and ENL HDDs
- All tiers in the Easy Tier array must contain devices with the same block size. All the SSDs and HDDs in the array must either be 528 bytes per sector or 4224 bytes per sector.
- Each tier in an Easy Tier array must contain at least 10% of the total disk capacity. For more information, see Estimating disk array capacities.
