MG9077

The MegaRAC© MG9077 is a Backplane Management Controller from American Megatrends, Inc. (AMI). Based on the most innovative management protocol in the field, Serial GPIO for SAS and SATA Host Bus Adapters, the MG9077 controller supports up to eight SAS/SATA drives with LED and enclosure management.

The MG9077 supports the emerging IBPI standard for SGPIO Interpretation, however the LED blinking pattern follows an interpretation defined by IBM. The MG9082 is a part that fully follows the IBPI standard.

What is an Enclosure or Backplane Management Controller

A backplane is a printed circuit board) that is specifically designed to connect hard disk drives to Server (computing) and Computer data storage systems.

Backplane LEDs

Backplanes are typically outfitted with Light Emitting Diodes LED to indicateparticular conditions. Usually 2 or 3 LEDs are used per drive (or slot).

Activity LED.This LED, usually Green, is used to indicate activity to the drive. Activity means that data is either read or written to the drive. Some equipment vendors will blink the LED at a steady rate during activity (i.e. at 4Hz), whereas others will actually turn the LED on and off synchronously with the actual activity.

Fail/Rebuild/Predicted Failure LEDThis LED, if it exists, is most often Red. It is turned ON where a failure of the drive is detected. Some vendors also use blinking variations of this LED to indicate a rebuild condition, or a predicted failure condition.

Locate LEDThis LED, when present, is typically Blue. It is turned on when a user selects a particular drive or drive slot through the storage management software. The locate LED is useful in locating a particular drive or drive-slot where there are large numbers of drives or banks of drives in large computer systems. Some vendors will blink the Locate LED rather than just illuminating it.

Because not all vendors equip every drive slot with 3 LED, combinations of LEDs and blinking patterns may be used to indicate various conditions. If 2 LEDs only exist per drive, the first is typically Activity LED and the second is Fail.

Typical Slot Drive States

ON-LINE - This is the normal operating condition for a drive. There is no failure detected and the drive can be accessed.

ACTIVITY - This LED either turns on when a drive is installed and blinks OFF with activity. This is done so that the single LED can both indicate that the slot is populated as well as the actual activity to the slot.

FAIL - A solid Red LED indicates a drive that has failed, and is no longer operational. The failure would most likely be a result of data that was unsuccessfully read from or written to the drive. This condition will remain until the drive is replaced or rebuilt. One can also manually "Fail" a drive, which is useful in testing, in which case there is nothing physically wrong with the drive. A manually failed drive can be rebuilt and brought back on-line.

REBUILDING - A drive that is part of a RAID-array can be rebuilt, which means that the data on the drive is in the process of being restored from redundant media. If the rebuild succeeds, the drive becomes ON-LINE after the Rebuild. If the rebuild is terminated or fails, the drive will become FAILed.

PREDICTED FAILURE - A drive may successfully write data after a number of failed attempts. This case could be an indication that the storage medium is going bad.An HBA or RAID Controller can query the drive for such problems, and flag the drive with the prediction that it could fail in the near future, although it is currently operational. This can be indicated i.e. by a fast blinking Red LED.

Driving LEDs

The MG9077 can drive LEDs directly, without the use of an external buffer amplifier. In this case, up to 16 LEDs can be driven directly. This is due to the limitation in IO-pins to 16. Since up to 8 drive and 3 LEDs per slot could be needed, the MG9077 can also use external buffers to drive up to 4 LEDs for each of the 8 slots, which means that 32 LEDs could be driven to represent a particular state.

SGPIO

SGPIO (Serial General-Purpose Input/Output) is a 4-signal (or 4-wire) bus used between a Host Bus Adapter (HBA) and a backplane. Out of the 4 signals, 3 are driven by the HBA and 1 is driven by the backplane. Typically, the HBA is a storage controller located inside a server, desktop, rack or workstation computer that interfaces with Hard Disk Drives (HDDs) to store and retrieve data.

The MG9077 supports 2 SGPIO channels. Multiple instances of the MG9077 can be cascaded so that drives on the same logical SGPIO-bus can be spanned across physical backplanes. This is especially useful in blade servers and high configurability systems, where a single backplane with few drives can be combined into larger storage arrays.

Links to Other Backplane Controllers

*MG9082 Backplane Management Controller With Dual SGPIO and IBPI

Related Links

* [ftp://ftp.seagate.com/sff/ SFF Documents] (Documents & Specifications)
* [ftp://ftp.seagate.com/sff/SFF-8485.PDF SFF-8485] SGPIO specification
* [ftp://ftp.seagate.com/sff/SFF-8489.PDF SFF-8489] IBPI specification
* [http://www.ami.com/products/catpage.cfm?CatID=14 Backplane Controllers from AMI]