for true cluster file system, d locks would be needed.(? don’t want
participating fs to communicate too much on the network). My question is how
far are we away from seeing dlocks getting implemented on all scsi disks.
Probably one could have notification method, whereby once disk is update
(prior to it also) and if the corresponding logical address is mapped by the
cache manager) cache manager is informed of this.I think its implementation
of oplocks using dlocks and some other low lever drivers.
-----Original Message-----
From: Jamey Kirby [mailto:xxxxx@storagecraft.com]
Sent: Friday, February 22, 2002 2:45 PM
To: File Systems Developers
Subject: [ntfsd] Re: How to share storage device on logical block acce ss
level?
I suspect it is not as much the cache manager, but how the current file
systems use the cache manager. To support shared disks, you will need a
whopping cache consistency and locking mechanism; similar to oplocks.
However, oplock are controlled on the server and in a SAN the device itself
is a server.
-----Original Message-----
From: xxxxx@lists.osr.com
[mailto:xxxxx@lists.osr.com] On Behalf Of Geoff Clow
Sent: Friday, February 22, 2002 2:27 PM
To: File Systems Developers
Subject: [ntfsd] Re: How to share storage device on logical block acce ss
level?
How does NT’s cache manager impede a shared device file system? The FS
controls whether a file is cached, and when that cache is flushed for cache
coherency. One problematic case is VMM mapped files, but disallowing shared
write access to mapped files seems a trivial restriction.
-----Original Message-----
From: Smith, Joel [mailto:xxxxx@ntpsoftware.com]
Sent: Friday, February 22, 2002 10:37 AM
To: File Systems Developers
Subject: [ntfsd] Re: How to share storage device on logical block acce ss
level?
Why, do you suppose, is there no commercial cluster file system for
Windows? It there something in the design of the OS that precludes the
development of a true cluster FS (perhaps this is intimated by your last
paragraph) or is there simply no commercial market for such a thing?
-Joel
-----Original Message-----
From: xxxxx@veritas.com [ mailto:xxxxx@veritas.com
mailto:xxxxx ]
Sent: Friday, February 22, 2002 8:17 AM
To: File Systems Developers
Subject: [ntfsd] Re: How to share storage device on logical block access
level?
On 02/21/02, ““Anton Kolomyeytsev” ” wrote:
> Hi,
>
> I have a storage device (hard disk) that is accessable from more then one
> machine in the same time (let’s assume it’s a SCSI hard disk on shared
> SCSI
> bus). While the device is only readen everything is OK, but how can I make
> this device writable by more then one client in the same time? How to keep
> the file caches consistant? Any ideas? Anybody works with clusters here?
> File system drive will not work I need to use existing one (maybe modified
> with filter driver but I’d prefer not to do so…)
>
> Regards,
> Anton
>
> P.S. For now I do store the written data in the different space so the
> hard
> disk is “partially shared”. Only the data that was never touched by
> writing.
>
> —
I worked on “Digital Clusters for Windows NT” several years ago, and we
determined that there was no simple answer. Thus we developed the
“sequential sharing” model for shared SCSI disk usage, which MSCS still
uses today. At any given time, only one node is allowed to access a shared
disk.
Many other people have replied, but only Andy Champ has given you a clue
about the answer. The answer is - you can’t do it without a true cluster
filesystem, running on all computers sharing the disk, and communicating
with each other. Other operating systems have achieved this in the past
(the classic is DEC’s VMS Clusters, released in 1984). But as of today, no
commercial cluster filesytem has been released for NT.
You could not get the right results with a simple filter driver, and might
even have troubles with a full filesytstem driver too, since the NT cache
manager is also involved in writing to disk.
Good luck!
Carl Appellof
VERITAS Software Global Corporation
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