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ServeRAID M1215 SAS/SATA Controller for IBM System x User’s Guide
Chapter 1: Overview
Benefits of the ServeRAID M1215 SAS/SATA Controller
1.5.6
Flexibility Features
These features increase the flexibility of the ServeRAID M1215 controller:
Supports a Flash ROM interface, a nonvolatile static RAM (NVSRAM) interface, and a pipelined synchronous burst
SRAM (PSBRAM) interface
Offers a flexible programming interface to tune I/O performance
Allows mixed connections to SAS targets or SATA III targets
Leverages compatible connectors for SAS connections and SATA III connections
Allows grouping of up to four PHYs in a single quad port to form a wide port
Allows programming of the World Wide Name
1.5.7
Protection Information (T10-DIF)
The T10 Technical Committee of the INCITS standardized the basic requirements to implement a data protection
model for end-to-end data protection. This model protects your data within a storage system from various sources of
corruption that historically have gone undetected. Examples of corruption sources include hardware datapath errors
(such as FIFO overruns and underruns), firmware errors (such as arithmetic overflow or incorrect pointer usage), and
external agents overwriting the data in memory.
A fundamental component of the T10 data protection model is the addition of 8 bytes of extra protection information
transferred with each block of user data in the storage system, as shown in the following figure. Although not
specifically named in the T10 standards, this collection of 8 bytes is commonly referred to as the DIF. The DIF contains
three distinct values: a 2-byte logical block guard, a 2-byte logical block application tag, and a 4-byte logical block
reference tag. The T10 specification defines four types of usage models of data protection: Type 0, Type 1, Type 2, and
Type 3 (refer to the most current revision of INCITS T10/1799-D for further information)
Figure 3 T10 Data Integrity Field for MegaRAID Protection Information
1.5.8
Drive Roaming
Drive roaming occurs when the physical disks are changed to different ports on the same controller. When the drives
are placed on different channels, the controller detects the RAID configuration from the configuration data on the
drives.
Configuration data is saved in both the NVRAM on the RAID controller and on the drives attached to the controller.
This action maintains the integrity of the data on each drive, even if the drives have changed their target ID.
NOTE
In a clustering environment, drive roaming is supported within the same channel only.
NOTE
If you move a drive that is being rebuilt, the rebuild operation restarts; it does not resume from where
the rebuild operation stopped.
