boot.msg contains the following:
=================================================================
<6> target4:0:1: FAST-20 WIDE SCSI 40.0 MB/s ST (50 ns, offset 31)
<5>  Vendor: WDIGTL    Model: WDE4550 ULTRA2    Rev: 1.22
<5>  Type:   Direct-Access                      ANSI SCSI revision: 02
<6> target4:0:1: tagged command queuing enabled, command queue depth 16.
<6> target4:0:1: Beginning Domain Validation
<6> target4:0:1: FAST-20 SCSI 20.0 MB/s ST (50 ns, offset 31)
<6> target4:0:1: FAST-20 WIDE SCSI 40.0 MB/s ST (50 ns, offset 31)
<6> 4:0:1:0: ODD transfer in DATA IN phase.
<6> 4:0:1:0: COMMAND FAILED (87 0 10).
<3> target4:0:1: Wide Transfers Fail
<6> target4:0:1: Domain Validation skipping write tests
<6> target4:0:1: FAST-20 SCSI 20.0 MB/s ST (50 ns, offset 31)
<6> target4:0:1: Ending Domain Validation
=====================================
against latest (2.6.13-9) source
diff /mot/save/scsi_scan.c scsi_scan.c
488d487
<               scsi_cmd[4] &= 0xFE; /* make sure it is an even transfer */
522,524c521
<               response_len = (unsigned char) inq_result[4] + 7; /* RJS */
<               response_len &= 0xFFFE; /* RJS make sure it is an even xfer */
<
---
>               response_len = (unsigned char) inq_result[4] + 5;

========================================
<6> target4:0:1: FAST-20 WIDE SCSI 40.0 MB/s ST (50 ns, offset 31)
<5>  Vendor: WDIGTL    Model: WDE4550 ULTRA2    Rev: 1.22
<5>  Type:   Direct-Access                      ANSI SCSI revision: 02
<6> target4:0:1: tagged command queuing enabled, command queue depth 16.
<6> target4:0:1: Beginning Domain Validation
<6> target4:0:1: FAST-20 SCSI 20.0 MB/s ST (50 ns, offset 31)
<6> target4:0:1: FAST-20 WIDE SCSI 40.0 MB/s ST (50 ns, offset 31)
<6> target4:0:1: Domain Validation skipping write tests
<6> target4:0:1: FAST-20 WIDE SCSI 40.0 MB/s ST (50 ns, offset 31)
<6> target4:0:1: Ending Domain Validation
========================================

Which properly enables wide transfers. This just fixes the probe on booting. The
SCSI code should be reviewed for installation of a lower level, selectable
enforcement of even sized buffers, possibly a debugging assert warning on odd
transfer to flag portability issues for these (admittedly older) WDE4550 drives.