Some users (me and a few others) have experienced lock ups in our
PowerBooks when SCSI emulation devices (ZuluSCSI, BlueSCSI, etc) are
spun down for power conservation and then subsequently spun back up.
SCSI2SD seems to not have this issue but it seems some folks using the
other two major brands (ZuluSCSI and BlueSCSI) have had issues. For
those of us having issues, it has occurred in System 7.1 through
System 7.5.5.
[ Why does it happen? (Working Theory) ]
It seems after power is restored to these SCSI emulators, the system
software will quickly (within 500ms) issue the IO request that caused
the SCSI emulator to be spun back up (ie. have its power restored). If
the SCSI emulator device isn't ready when this IO request comes in,
you get into this hung state because the SCSI emulator misses the
request and sits around waiting for a request, whereas the system
software issued the request and sits around waiting for a response.
This lockup lasts for 180 seconds after which the system finally
unfreezes.
[ Why are some devices ok? ]
I believe it's all in the timing. If the device can become operational
before the IO request comes in, you're all good. Some devices (and/or
their firmware version) either get ready quickly or get into a state
where it can read and hold the IO request until the device is fully
ready to go (ie. don't miss the request). I have not been able to
reproduce the issue with a SCSI2SD device. It's possible that's
because SCSI2SD uses the SD card as a raw disk whereas ZuluSCSI and
BlueSCSI have an extra layer (filesystem) from which it exposes
multiple disks. Or it could be those other two devices offer more
features and it takes more time to get ready? I have heard newer
BlueSCSI's might be ok? If you aren't having these issues, awesome!
But if you are, continue reading.
[ SD Aide ]
SD Aide is a system extension / control panel which intercepts the HD
spin up function in the system software and after spin up, adds a
configurable delay to allow the device to finish booting before the IO
request is sent. This ensures the SCSI emulator device does not miss
the request so that your PowerBook isn't locked up for 3 minutes every
time the disk is spun down. You can of course just disable spin down
but this option doesn't exist in System 7.1 through 7.1.1, and that
wouldn't help with sleep mode.
Just drop SD Aide into your control panel folder, double click it and
configure the delay you want, and then reboot. The ZuluSCSI devices I
have used (stock configuration) seem to like 2-3 seconds of delay. The
BlueSCSI device that a friend has wanted a 4 second delay.
[ Requirements ]
SD Aide only runs on System 7 or greater, only on 68K, and only on
Macintoshes that have a power manager implementation (ie. PowerBooks).
[ Testing ]
SD Aide has been tested on System 7.1, 7.1.1, 7.1.2, and 7.5.5. It has
been tested on a PowerBook 540c, PowerBook 170, and a PowerBook 160.
It has been tested with a ZuluSCSI 1.1 Laptop Edition, a BlueSCSI
device, and a SCSI2SD (although it didn't need it).
