Cheap Way To Share Fibre Channel Storage

I'm looking for a cheap way to have more than one computer share
read-only access to fibre channel storage under Windows 2000.
I'm using Compaq fibre channel arrays for the hardware, and those
are fine for low-end use, but they don't have any option
internally to give read-only access. A host is designated in
the Compaq software as either having full access or no access.
If multiple Windows hosts try to write to the same logical
device, they will trash sensitive file system structures on the
disk.

Is there any low-priced software that would run as a service on
Windows that would prevent any attempt to write to designated
disks? The service would need to be fairly low level and would
need to prevent the Windows kernel from writing to the disk.

--
Will
Internet: westes at earthbroadcast.com

I tried this in the past. It turns out that NTFS won't even mount a LUN
that declares itself to be Read-Only. In the end we put an ugly hack
into the array firmware that pretended to accept writes from the
servers but then just threw them away. The problem with this is that it
works too well, because the servers do some local buffering; When the
users on the servers "wrote" new files to the read-only array it
actually seemed as if the files were being written. Their icons
appeared, and when they re-opened those files they contained the right
contents - except that they were all being served up from the local
buffer, rather than coming from the array. Needless to say, when the
LUN was unmounted and then remounted the users were very surprised to
see none of their newly written files.

So you have to either find a way to do a read-only mount, or just make
all file access go through a centralized CIFS or NFS server where you
can do access control.



On 2005-05-28 12:13:01 -0700, "Will" said:

I'm looking for a cheap way to have more than one computer share
read-only access to fibre channel storage under Windows 2000.
I'm using Compaq fibre channel arrays for the hardware, and those
are fine for low-end use, but they don't have any option
internally to give read-only access. A host is designated in
the Compaq software as either having full access or no access.
If multiple Windows hosts try to write to the same logical
device, they will trash sensitive file system structures on the
disk.

Is there any low-priced software that would run as a service on
Windows that would prevent any attempt to write to designated
disks? The service would need to be fairly low level and would
need to prevent the Windows kernel from writing to the disk.

palomina wrote in message ...

I tried this in the past. It turns out that NTFS won't even mount a LUN
that declares itself to be Read-Only. In the end we put an ugly hack

WinNT4 did have that bug with read-only, Microsoft claims it was fixed in
Win2K.

The application is a flight simulation system that requires several
computers to act together loading large numbers of files that provide
terrain and texture data. So we won't have "users" trying to write files
to these file systems. What you describe sounds perfect for our
application.

Which array were you using, and is the "hack" a published one?

--
Will
Internet: westes AT earthbroadcast.com


palomina wrote in message ...

I tried this in the past. It turns out that NTFS won't even mount a LUN
that declares itself to be Read-Only. In the end we put an ugly hack
into the array firmware that pretended to accept writes from the
servers but then just threw them away. The problem with this is that it
works too well, because the servers do some local buffering; When the
users on the servers "wrote" new files to the read-only array it
actually seemed as if the files were being written. Their icons
appeared, and when they re-opened those files they contained the right
contents - except that they were all being served up from the local
buffer, rather than coming from the array. Needless to say, when the
LUN was unmounted and then remounted the users were very surprised to
see none of their newly written files.

So you have to either find a way to do a read-only mount, or just make
all file access go through a centralized CIFS or NFS server where you
can do access control.

I tried this in the past. It turns out that NTFS won't even mount a LUN
that declares itself to be Read-Only.

Fixed in XP and w2k3.

--
Maxim Shatskih, Windows DDK MVP
StorageCraft Corporation

http://www.storagecraft.com

Will wrote:
I'm looking for a cheap way to have more than one computer share
read-only access to fibre channel storage under Windows 2000.
I'm using Compaq fibre channel arrays for the hardware, and those
are fine for low-end use, but they don't have any option
internally to give read-only access. A host is designated in
the Compaq software as either having full access or no access.
If multiple Windows hosts try to write to the same logical
device, they will trash sensitive file system structures on the
disk.

Is there any low-priced software that would run as a service on
Windows that would prevent any attempt to write to designated
disks? The service would need to be fairly low level and would
need to prevent the Windows kernel from writing to the disk.


Cisco MDS switches support read-only zones. I believe its a licensed
feature. Not exactly cheap if you don't already own Cisco fibre channel
switches, but I thought it was worth mentioning.

Curious how a FC switch would have any knowledge of the file system, file
name, the SCSI block allocation per file, so it could implement file system
"read only" locking? Very curious....
"Jon Metzger" wrote in message
...
Will wrote:
I'm looking for a cheap way to have more than one computer share
read-only access to fibre channel storage under Windows 2000.
I'm using Compaq fibre channel arrays for the hardware, and those
are fine for low-end use, but they don't have any option
internally to give read-only access. A host is designated in
the Compaq software as either having full access or no access.
If multiple Windows hosts try to write to the same logical
device, they will trash sensitive file system structures on the
disk.

Is there any low-priced software that would run as a service on
Windows that would prevent any attempt to write to designated
disks? The service would need to be fairly low level and would
need to prevent the Windows kernel from writing to the disk.


Cisco MDS switches support read-only zones. I believe its a licensed
feature. Not exactly cheap if you don't already own Cisco fibre channel
switches, but I thought it was worth mentioning.

"Will" wrote in message
...

Is there any low-priced software that would run as a service on
Windows that would prevent any attempt to write to designated
disks? The service would need to be fairly low level and would
need to prevent the Windows kernel from writing to the disk.

Even if such a utility exists, it will not help you because you need all the
systems in "share" group to be aware of writes, even if only one of them is
allowed to write. The reason is that the read-only machines may get stale
data from the disk because the "writer" has cached writes not yet committed
to disk that may impact filesystem structures or file content. You could
also get problems with writes that are partially complete when one of the
readers tries to read.

The only way this can be done safely is with a shared filesystem designed
for the task. On Windows you should look at Tivoli SANergy as possible
solution, see

http://www-306.ibm.com/software/tivo...ducts/sanergy/


--
Nik Simpson

No, our application is write once every two weeks, but read
10,000 times a day. We don't need to track writes to the disk,
and on those days when writes take place, the readers can simply
be rebooted.

I really do need something very very simple.

--
Will
Internet: westes at earthbroadcast.com


"Nik Simpson" wrote in message
news

"Will" wrote in message
...

Is there any low-priced software that would run as a service
on
Windows that would prevent any attempt to write to designated
disks? The service would need to be fairly low level and
would
need to prevent the Windows kernel from writing to the disk.

Even if such a utility exists, it will not help you because you
need all the
systems in "share" group to be aware of writes, even if only
one of them is
allowed to write. The reason is that the read-only machines may
get stale
data from the disk because the "writer" has cached writes not
yet committed
to disk that may impact filesystem structures or file content.
You could
also get problems with writes that are partially complete when
one of the
readers tries to read.

The only way this can be done safely is with a shared
filesystem designed
for the task. On Windows you should look at Tivoli SANergy as
possible
solution, see

http://www-306.ibm.com/software/tivo...ducts/sanergy/


--
Nik Simpson

On Sun, 12 Jun 2005 11:21:05 -0700, "Will"
wrote:

No, our application is write once every two weeks, but read
10,000 times a day. We don't need to track writes to the disk,
and on those days when writes take place, the readers can simply
be rebooted.

I really do need something very very simple.

I've heard there is some sort of registry setting or add-in that would
allow you to do a Read-only NTFS mount. Can't get much simpler than
that.