|C H A P T E R 4|
Overview of Integrated Striping
This chapter provides an overview of the LSI Integrated Striping (IS) feature. It includes these sections:
The LSI Integrated Striping (IS) feature is useful for applications that require the faster performance and increased storage capacity of striping. The low-cost IS feature has many of the advantages of a more expensive RAID striping solution. A single IS logical drive may be configured as the boot disk or as a data disk.
The IS feature is implemented with controller firmware that supports the Fusion-MPT Interface. IS provides better performance and more capacity than individual disks, without burdening the host CPU. The firmware splits host I/Os over multiple disks and presents the disks as a single logical drive. In general, striping is transparent to the BIOS, the drivers, and the operating system.
The SAS BIOS CU is used to configure IS volumes, which can consist of two to ten disks.
IS includes the following features:
|Note - All physical disks in a volume must be connected to the same SAS controller.|
The IS feature writes data across multiple disks instead of onto one disk. This is accomplished by partitioning each disk’s storage space into 64 Kbyte stripes. These stripes are interleaved round-robin, so that the combined storage space is composed alternately of stripes from each disk.
For example, as shown in FIGURE 4-1, segment 1 is written to disk 1, segment 2 is written to disk 2, segment 3 is written to disk 3, and so on. When the system reaches the end of the disk list, it continues writing data at the next available segment of disk 1.
FIGURE 4-1 Integrated Striping Example
FIGURE 4-2 shows a logical view and a physical view of Integrated Striping configuration.
FIGURE 4-2 Integrated Striping - Logical and Physical Views
The primary advantage of IS is speed, because it transfers data to or from multiple disks at once. However, there is no data redundancy; therefore, if one disk fails, that data is lost.
This section describes features of the LSI Integrated RAID firmware.
The firmware supports metadata, which describes the IS logical drive configuration stored on each member disk. When the firmware is initialized, each member disk is queried to read the stored metadata to verify the configuration. The usable disk space for each IS member disk is adjusted down when the configuration is created, in order to leave room for this data.
SMART is a technology that monitors disk drives for signs of future disk failure and generates an alert if such signs are detected. The firmware polls each physical disk in the volume at regular intervals. If the firmware detects a SMART ASC/ASCQ code on a physical disk in the IS volume, it processes the SMART data and stores it in nonvolatile memory. The IS volume does not support SMART directly, since it is just a logical representation of the physical disks in the volume.
Disk write caching is enabled by default on all IS volumes.
The BIOS uses the LSI Fusion-MPT interface to communicate to the SAS controller and firmware to enable IS. This includes reading the Fusion-MPT configuration to gain access to the parameters that are used to define behavior between the SAS controller and the devices connected to it. The Fusion-MPT drivers for all supported operating systems implement the Fusion-MPT interface to communicate with the controller and firmware.