unique worldwide tape names

Witalka, Jerome J RV jjw1 at PO9.RV.unisys.com
Tue Aug 20 05:56:00 PDT 1996


* From the SCSI Reflector, posted by:
* "Witalka, Jerome J           RV" <jjw1 at PO9.RV.unisys.com>
*

>From below:
"5. Multiple paths to the same device certainly exists. However,
multi-pathing is totally limitted to a server (single computer or   
cluster).
Having multiple paths to a device is like having multiple entrances to a
house. Except for shared disk applications like OPS, only one path is   
active
at the same time."

The Unisys 2200 operating system supports multiple simultaneous copies of   
the operating system running in separate Host systems, each running   
concurrent IOs to an individual device. We call this concept multi-host   
file sharing.

If the Fibre channel drop is a controller, the 2200 operating system   
supports multiple concurrent IOs to different devices via multiple paths   
to the control unit within a single copy of the OS.


Jerry Witalka  M.S. 4873                 EMail:jjw1 at po9.rv.unisys.com
Unisys Corporation                          Voice:  612-635-7958
P.O. Box 64942
 St. Paul, MN 55164-094

 ----------
From:  scsi-owner[SMTP:scsi-owner at Symbios.COM]
Sent:  Monday, August 19, 1996 10:52 AM
To:  ieee+mss; wrenn; buck; Smith, Greg
Cc:  fc; scsi
Subject:  Re: unique worldwide tape names

* From the SCSI Reflector, posted by:
* Bob Baird <bbaird at hpmfas3.cup.hp.com>
*
To SSSWG followers,

Since I seem to have created some controversy, I guess I should clarify   
my
position. This will probably create more controversy --- good.

I agree that addressing and naming are two different aspects of an   
object.
However, they are not as different in practice as they seem. Also, most
names are only meaningful within a context. The following summarizes my
position:

1. I think we should consolidate device ADDRESSING around IP or a   
compatible
extension to IP. I believe that network attached devices are the way to   
go.

2. I think that "device-files' should have names like normal files and be
represented like normal files in a file-system directory. By   
"device-file",
I mean a linear sequence of bytes on a unit of media having no   
file-system
structure. Files on tapes and database files on a raw disk partitions are
two examples of device-files. An application should be able to open
device-file through the (Unix or NT) file directory and access the file   
with
normal file semantics. In this case, user's would know the name of a
device-file just like they know the name of any other file. Do we wish to
give universally unique names to normal files too? If so, device-files   
and
normally files should be treated equally. If there is a need for UUIDs   
for
device-files, the same should apply to  normal files.

3. The first part of the IP address (depending on whether it is type 1,   
2,
or 3) is already a customer id of sorts. There is already a committee to
assign those numbers. Why not use them for UUIDs and remove the need for
another committee? Do we believe that tapes physically travel between
customers so much that we need another standard for it?

4. Given my assumptions that raw "device-files" should be named in file
directories, do we really need UNIVERSAL identifiers for removable media?
Isn't  file name plus server sufficient for locating a tape, CDROM, disk
partition, MO, etc. device-file? Once the device-file is located by
file-name it can be addressed by IP.

5. Multiple paths to the same device certainly exists. However,
multi-pathing is totally limitted to a server (single computer or   
cluster).
Having multiple paths to a device is like having multiple entrances to a
house. Except for shared disk applications like OPS, only one path is   
active
at the same time.

6. I definitely agree that media verification standards should exist   
withing
a site. Yes, you must know which paths lead to the same destination.
However, I am not convinced that volume labelling is the only way to
validate paths or that media labels must be universally unique.


This is a fun controversy, but I need to get on with HP work right now.


Bob
Bob Baird
Hewlett-Packard Company
General Systems Divison, GSSL
19111 Pruneridge Avenue, MS 44UB
Cupertino, CA 95014
voice:  408-447-7084
fax:    408-447-1345






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