Two computers sharing a external hard drive at the same time

Hi All,

I have a external hard drive (USB Lacie) and two computers (windows and
Linux). I wanted the two compters to share the external hard drive at
THE SAME TIME.
Is it possible?

Any help is greatly apprecieated.
Thanks

Ying

In article <R48mc.216$(E-Mail Removed)>,
Ying Hu <(E-Mail Removed)> wrote:

> I have a external hard drive (USB Lacie) and two computers (windows and
> Linux). I wanted the two compters to share the external hard drive at
> THE SAME TIME.
> Is it possible?

I've never heard of it being possible, with the exception of some Macintosh
Powerbooks which were connected to a desktop via SCSI while on.

Consider connecting it to only one machine directly, and sharing it over the
network on that machine.

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Hactar wrote:
> In article <R48mc.216$(E-Mail Removed)>,
> Ying Hu <(E-Mail Removed)> wrote:
>
>>I have a external hard drive (USB Lacie) and two computers (windows and
>>Linux). I wanted the two compters to share the external hard drive at
>>THE SAME TIME.
>>Is it possible?
>
> I've never heard of it being possible, with the exception of some Macintosh
> Powerbooks which were connected to a desktop via SCSI while on.
>
> Consider connecting it to only one machine directly, and sharing it over the
> network on that machine.

Yeah, don't make your life more difficult, go with Hactar, use nfs or
smb or whatever you prefer

On Wed, 05 May 2004 11:52:17 -0400, Ying Hu wrote:
> I have a external hard drive (USB Lacie) and two computers (windows and
> Linux). I wanted the two compters to share the external hard drive at
> THE SAME TIME.

This may fit a literal definition of "networking", but we're not that
literal around here. This is a hardware question, way OT here.

> Is it possible?

A long time ago with SCSI devices I discovered that it is technically
possible to share a SCSI bus among multiple machines, as long as each
device on the bus, INCLUDING THE HOST ADAPTERS, has a distinct SCSI ID.
USB storage devices are handled as SCSI in Linux, and probably Windows
as well. The question then becomes, "Do USB controllers appear on the
virtual SCSI bus as a host adapter, and if so, can you set the SCSI ID
to something nonstandard?"

My bet is that it will work just fine, but watch out for simultaneous
accesses! There's no locking. This is the kind of thing where you'd
want to be very careful. For best results have one OS mount the
filesystem read-only ... and since I doubt that's possible in a
crippled OS like Windows, I guess the Linux machine will have to do it.
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/dev/rob0 wrote:
> On Wed, 05 May 2004 11:52:17 -0400, Ying Hu wrote:
>
>>I have a external hard drive (USB Lacie) and two computers (windows and
>>Linux). I wanted the two compters to share the external hard drive at
>>THE SAME TIME.
>
>
> This may fit a literal definition of "networking", but we're not that
> literal around here. This is a hardware question, way OT here.
>
>
>>Is it possible?
>
>
> A long time ago with SCSI devices I discovered that it is technically
> possible to share a SCSI bus among multiple machines, as long as each
> device on the bus, INCLUDING THE HOST ADAPTERS, has a distinct SCSI ID.
> USB storage devices are handled as SCSI in Linux, and probably Windows
> as well. The question then becomes, "Do USB controllers appear on the
> virtual SCSI bus as a host adapter, and if so, can you set the SCSI ID
> to something nonstandard?"
>
> My bet is that it will work just fine, but watch out for simultaneous
> accesses! There's no locking. This is the kind of thing where you'd
> want to be very careful. For best results have one OS mount the
> filesystem read-only ... and since I doubt that's possible in a
> crippled OS like Windows, I guess the Linux machine will have to do it.

The file systems on such drives will be clobbered in a fraction of a
second, if there is no co-operation of the operating systems: if
both computers b8uffer the disk sectors independently, the crucial
file system sectors (which are the most used) will very soon end up
unsychronised.

I have worked with one system with twin Data General CPU's and common
disks - it's bloody complicated. There was a special communication
interface in both computers to aid the kernels to synchronise.
The system was built before the time of current networks. Please
follow the networking route for shared disk units - it's the thing
that works.

HTH

Tauno Voipio
tauno voipio @ iki fi

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In comp.os.linux.networking Ying Hu <(E-Mail Removed)> suggested:
> Hi All,

> I have a external hard drive (USB Lacie) and two computers (windows and
> Linux). I wanted the two compters to share the external hard drive at
> THE SAME TIME.
> Is it possible?

Sure, just put the drive on the Linux box and share the mounted
fs using samba (www.samba.org), comes with most distro, perhaps
it's already installed and you just need to configure/start it?

Good luck

--
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Remove +SIGNS and www. if you expect an answer, sorry for
inconvenience, but I get tons of spam.
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"/dev/rob0" <(E-Mail Removed)> wrote in message news:<(E-Mail Removed)>...
> On Wed, 05 May 2004 11:52:17 -0400, Ying Hu wrote:
> > I have a external hard drive (USB Lacie) and two computers (windows and
> > Linux). I wanted the two compters to share the external hard drive at
> > THE SAME TIME.
>
> This may fit a literal definition of "networking", but we're not that
> literal around here. This is a hardware question, way OT here.
>
> > Is it possible?

I don't think so.

>
> A long time ago with SCSI devices I discovered that it is technically
> possible to share a SCSI bus among multiple machines, as long as each
> device on the bus, INCLUDING THE HOST ADAPTERS, has a distinct SCSI ID.
> USB storage devices are handled as SCSI in Linux, and probably Windows
> as well. The question then becomes, "Do USB controllers appear on the
> virtual SCSI bus as a host adapter, and if so, can you set the SCSI ID
> to something nonstandard?"

Can you set your motherboard to be a USB slave?

>
> My bet is that it will work just fine, but watch out for simultaneous
> accesses! There's no locking. This is the kind of thing where you'd
> want to be very careful. For best results have one OS mount the
> filesystem read-only ... and since I doubt that's possible in a
> crippled OS like Windows, I guess the Linux machine will have to do it.

My bet is that you can't fit two brains in one head and two USB root
hubs in one USB bus.

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In comp.os.linux.networking Tauno Voipio <(E-Mail Removed)> suggested:
> /dev/rob0 wrote:
> > On Wed, 05 May 2004 11:52:17 -0400, Ying Hu wrote:
> >
> >>I have a external hard drive (USB Lacie) and two computers (windows and
> >>Linux). I wanted the two compters to share the external hard drive at
> >>THE SAME TIME.
[..]

> >>Is it possible?

Yep, albeit not with your hardware. Just setup samba, as already
written.

[..]

> > My bet is that it will work just fine, but watch out for simultaneous
> > accesses! There's no locking. This is the kind of thing where you'd
[..]

> The file systems on such drives will be clobbered in a fraction of a
> second, if there is no co-operation of the operating systems: if
> both computers b8uffer the disk sectors independently, the crucial
> file system sectors (which are the most used) will very soon end up
> unsychronised.

That's very likely to happen, please don't try this out if the
data has any worth with your USB disk.

> I have worked with one system with twin Data General CPU's and common
> disks - it's bloody complicated. There was a special communication

Try a google search on "TruCluster", those have even shared /
and yep, it's not that easy...

--
Michael Heiming - RHCE (GPG-Key ID: 0xEDD27B94)

Remove +SIGNS and www. if you expect an answer, sorry for
inconvenience, but I get tons of spam.
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Ying Hu wrote:

> Hi All,
>
> I have a external hard drive (USB Lacie) and two computers (windows and
> Linux). I wanted the two compters to share the external hard drive at
> THE SAME TIME.
> Is it possible?

It theory it's possible, but it's not practical. That was often done years
ago, with mini-computers, but you need some method to arbitrate access. In
the Data General systems I worked on, the disk adapter board supported 2
controllers, but included a locking mechanism, to prevent simultaneous
access. A better bet, would be to share the drive over a network.

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Hactar wrote:

> I've never heard of it being possible, with the exception of some
> Macintosh Powerbooks which were connected to a desktop via SCSI while on.
>

It was common with mini-computers. I used to support Data General & DEC
(Digital Equipment Corporation) computers, among others, which did it.
However, it requires some arbitration method, to prevent both computers
from accessing the disk at the same time.
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To reply to this message, replace everything to the left of "@" with
james.knott.