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Method of detecting shorted SCSI bus ID lines with devices having unique serialization

IP.com Disclosure Number: IPCOM000014979D
Original Publication Date: 2001-Aug-01
Included in the Prior Art Database: 2003-Jun-20
Document File: 2 page(s) / 41K

Publishing Venue

IBM

Abstract

Method of detecting shorted SCSI bus ID lines with devices having unique serialization

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Method of detecting shorted SCSI bus ID lines with devices having unique

serialization

Disclosed is a method for determining existence of unique SCSI (Small Computer System Interface) devices in the presence of a defect (short on an address line).

The problem with the SCSI bus used to connect storage peripherals on computer systems is in the presence of a short between one of the SCSI ID bus lines. The power or ground on a SCSI Enclosure Services (SES) backplane can "trick" the system into thinking that it has two physical SCSI devices at different SCSI addresses. Whereas, only one device actually exists, because when the SCSI device configuration tool "walks" the SCSI bus to inquire if there are physical storage devices present at each SCSI ID on a SCSI controller, it is looking for a response from each device and its data indicating the type of device at that address, etc. However, it does not actually try to determine if there is a unique device present at each SCSI ID address. For example, if the most significant bit of SCSI ID bus line is shorted to ground ("low" logic level) on a SES backplane containing no physical device, when the system "walked" the SCSI bus, it would look like there were two physical SCSI devices present at two different SCSI addresses differing in addresses only by this high-order bit. However, if there was an actual SCSI device at the address where the high order bit of the SCSI ID, it would purposely be assigned to a low logic value (assigned by slot position in the SES backplane):

For Example:

1101 <-------Normal SCSI address of empty slot in SES (slot 14) 0101 <-------Apparent SCSI address of slot 14 in presence of short to ground of most-significant SCSI address bit. 0101 <-------Actual SCSI address of SCSI device in S...