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The following is an archive of a post made to our 'vox-tech mailing list' by one of its subscribers.

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Re: [vox-tech] brain dead hardware question: power pc vs x86 scsi
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Re: [vox-tech] brain dead hardware question: power pc vs x86 scsi



On Sun, 9 Sep 2001, Peter Jay Salzman wrote:
> can power pc scsi devices be used on x86 scsi systems?

A majority of the time with most devices (when measured as raw quantity,
not necessarily when measured by "class" of devices - Storage, scanner,
Adapters) the answer would be yes.

I don't think Linux supports HFS+ yet, but does support HFS. If that
SyQuest drive was formatted HFS+ you may not be able to mount the disk.

Also, check out info for SyQuest unless others here have suggestions on
them. With -Zip- Disks, you mount partition 4 to read/write to
them. (Example: if your zip is on /dev/hdd, then you would mount
/dev/hdd4) I am not sure if SyQuest SCSI disks for Linux are like this,
someone else ight be able to offer info on this.

One thing with laptop SCSI on PCMCIA is power. Desktop based cards seem to
be better at pushing greater distances of cable with daisy-chained SCSI
deviced while laptops seem to lack the power, or shielding, or ? to deal
with the longer busses. (If you have lots of devices on a bus connected to
a laptop and they dont work, shorten the bus and remove some devices and
remoboot to see if it starts working.)

You probably know this next stuff, but I'll say it anyway for those
unintiated withy SCSI:

Make sure your SCSI Devices are all connected to the SCSI bus and turned
on before powering up the computer

Make sure both ends of the SCSI bus are "terminated"
Don't terinate devices in the middle of the bus, only the ends are
terminated.

Make sure there are no "splits" or "Y-s" in the SCSI bus, the bus is
linear, hence the name "bus" ;-)

Make sure no two devices share he same SCSI ID

Make sure you do not exceed length restrictions for your version and type
of SCSI.

It is not a good idea to mix SCSI-3 (68 pin) controllers with the older
50-pin devices when using special adapters that do SCSI-3 to
SCSI-2. (Extra control lines are lost on the bus, and this may cause
problems with some 68-pin SCSI-3 devices.) If you can afford it, get a
separate controler for the SCSI-2 devices, or a special SCSI-3 card that
offers dual channel  SCSi with SCSI-3 and SCSI-2. I have seen these
adapters work, but I still do not suggest it - esp. for servers.

If you want you bus to remain fast, keep the bus cables as short as
possible without making connections too short so they violate the
standard, and try to use similar speed devices on the bus. (Say 3 160MB/s
LVD2 drives together are better than the same drives plus 10MB/s CD-R
drives, and a few 20MB/s tape drives added to the same bus)

Convention suggests giving the SCSI controller ID "7". You can alter this
on many controllers, but it is not advised unless you have a really good
reason.

Convention suggests giving SCSI ID 0 to the first HD in the bus especially
if that is your boot drive.

Those 25-pion SCSI connectors are not part of the SCSI standard. Sure
Apple used them on lots of their boxes and IOMega used them on the SCSI
and ZIP+ drives, but they are cheating when they do. Whet they do is
combine several independednt ground lines into only a few so that each
previously independent ground now is shared. Though SCSI is rather robust
in many cases and can even "work" with risk/loss in performance without
ermination, and seem just fine with the 25-pin connectors, they are not
part of the official pinout standard AFAIK.

When you are rich, you might buy the fastest SCSI based RAID cards and
put your system disk on one RAID array. A second RAID array on a second
controller can be used for storage in the case of file servers, a third
bus using SCSI would have any CD-ROM devices that might share CDs to the
network, and a sepaate SCSI bus would include any tape drives.

Of course there is more to SCSI than this, but the above is prob enough to
get anyone on the list more knowledge on it than many people presently
using SCSI. :-)

-ME

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     Systems Department Operating Systems Analyst for the SSU Library


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