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File Corruption with SCSI Manager 4.3

Q: We are using SCSI Manager 4.3 on a Quadra 840. When SCSI Manager 4.3 is active (resident in the Extensions folder), we are experiencing a lot of problems -- mostly system hangs and data corruption in files. We ran tests to isolate these problems, using a variety of scenarios. In all the scenarios, the problems only occurred when SCSI Manager 4.3 was active.

When file corruption occurs, it is always in the first 16 bytes of a disk block. This area is overwritten by data that belongs in another area which is in offset 4096 bytes (400H) before the damaged area.

Is this a known problem, and if so, is there an update or patch for SCSI Manager 4.3?

A: This bug was identified and has been fixed in System 7.5.1 (System 7.5 with the update).

If a device goes bus-free after the command phase, the SCSI Manager 4.3 crashes. With the System 7.5 update applied, the SCSI Manager does not dispatch the next command if the bus is free after the earlier command. Also, SCSI Manager 4.3 in System 7.5 mistakenly tries to optimize TIBs on machines that do not have DMA, which could potentially cause data loss. TIB optimization is now turned off for pseudo-DMA machines.

For more information, see also: Technote OS 07.

[Jul 01 1995]

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