Browse Prior Art Database

Safe Power-Down Seqence for Storage Sub-System

IP.com Disclosure Number: IPCOM000114222D
Original Publication Date: 1994-Nov-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 48K

Publishing Venue

IBM

Related People

Morris, N: AUTHOR [+3]

Abstract

In a simple, low-cost storage sub-system the requirement to store data without any possibility of corruption can be difficult and expensive to meet. For example, in the event of a power-supply failure, the system could suddenly stop writing customer data, leaving an incomplete, corrupt sector.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 66% of the total text.

Safe Power-Down Seqence for Storage Sub-System

      In a simple, low-cost storage sub-system the requirement to
store data without any possibility of corruption can be difficult and
expensive to meet.  For example, in the event of a power-supply
failure, the system could suddenly stop writing customer data,
leaving an incomplete, corrupt sector.

      One approach is to provide electronic circuitry to monitor the
status of power-supplies (and/or other components) so that it can
give the logic in the storage media an Early Power-Off Warning (EPOW)
signal.  Where the host computer is connected by a SCSI cable, the
storage sub-system would then assert a SCSI reset to halt all
operations.

      This approach deals effectively with a true power-cut
situation, but has some disadvantages if the EPOW is due to a failing
power-supply or cooling fan.  The host SCSI bus would be held
permanently in a reset state, halting any activity for other devices
that might share the same SCSI bus.  Also, if the failing component
is a cooling fan, if it is not repaired quickly then the storage
media may overheat and be permanently damaged.

      By including two simple time delay circuits in the control
logic, the system can be made to shut down in the following sequence:
  1.  EITHER: An EPOW sense line from a power-supply goes active
       OR: A cooling fan failure sense line goes active.
  2.  A SCSI reset is immediately asserted by the shutdown logic.
  3. ...