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- Newsgroups: comp.sys.next.sysadmin
- Path: sparky!uunet!haven.umd.edu!ni.umd.edu!sayshell.umd.edu!louie
- From: louie@sayshell.umd.edu (Louis A. Mamakos)
- Subject: Re: WangDAT: How to fseek() ?
- Message-ID: <1992Jul29.233415.26017@ni.umd.edu>
- Keywords: cron
- Sender: usenet@ni.umd.edu (USENET News System)
- Nntp-Posting-Host: sayshell.umd.edu
- Organization: University of Maryland College Park
- References: <nq9sp2o@zuni.esd.sgi.com> <1992Jul28.215226.9960@ni.umd.edu> <1992Jul29.112201.9064@mic.ucla.edu>
- Date: Wed, 29 Jul 1992 23:34:15 GMT
- Lines: 45
-
- In article <1992Jul29.112201.9064@mic.ucla.edu> iwelch@agsm.ucla.edu (Ivo Welch) writes:
- >
- >> There is no "built-in" support for random seeking to blocks on DAT
- >> tape media, but it is not too difficult to issue "raw" SCSI commands
- >> to the tape driver with the appropriate commands to perform the
- >> seeking.
- >
- >Yes, but the question remains: WHAT ARE THE COMMANDS TO DO SO FOR WANGDATS?
-
- Well, I don't know what they are on a WangDAT drive; the code that I
- wrote for an Archive Python uses the SCSI-2 standard positioning
- commands for sequential access devices. The specific commands are
- LOCATE (0x2B) and READ POSITION (0x34). You use the MTIOCSRQ ioctl to
- issue raw SCSI commands to the tape device that you have open.
-
- >(I got 4 messages asking me to forward any responses; unfortunately I have not
- >received any). Again, has anybody written C functions that can substitute for
- >fseek() and ftell() (probably over the whole tape, rather than a file, which
- >would be just fine).
-
- Well, you can't write direct substitutes for fseek() and ftell() which
- return file positions which on the NeXT (and most UNIX platforms) are
- byte offsets. The code that I wrote treats the 4 byte quantities
- returned by LOCATE as opaque values; it turns out that they (on the
- Archive Python, at least) number tape blocks, including file marks.
- That's why I mentioned that you need someway to construct a database
- or index of these values, preferably while you are writing the tape.
-
- >I can no longer get a hold of the author of Safteynet, nor will Safetynet do
- >what I need: maintaining data-bases to be read by programs. I do not primarily
- >want to increase dump/tar/etc speed!!
-
- You can try <brian@Systemix.COM> to get further information about the
- SafetyNet program. Alternatively, you can get get the OEM or
- programmer's manual for the WangDAT drive and/or a SCSI-2 speci and
- combine that with 'man 4 st' and 'man 4 sg' to hack up some code to do
- what you'd like.
-
- As I mentioned, I don't know for certain if the WangDAT uses LOCATE
- and READ POSITION commands or some vendor specific commands. The
- Archive Python, for instance, provide the SCSI-2 LOCATE/READ POSITION
- as well as some vendor specific commands that do much the same sort of
- thing, but the tape positions are encoded differently.
-
- louie
-