Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!sobeco!roe
From: roe@sobeco.com (r.peterson)
Newsgroups: comp.sys.mips
Subject: Re: Experience with DAT drives?
Message-ID: <1990Apr9.183829.16768@sobeco.com>
Date: 9 Apr 90 18:38:29 GMT
References: <798@cluster.cs.su.oz>
Distribution: comp
Organization: Sobeco Group - Montreal, Canada
Lines: 105

From article <798@cluster.cs.su.oz>, by yar@cs.su.oz (Ray Loyzaga):
> In article <1990Mar28.053504.14178@sobeco.com> roe@sobeco.com (r.peterson) writes:
>> Hmmm... I've had no problems whatever with the WANGDAT drive - passes
>> all boot tests, and can be used to both boot and install the
>> operating system (both miniroot and the full distribution).
>> 
> 
> The drive I tested made the SCS master test fail.
> 

Hmmm - thats' kind of interesting - what drive and revision level are you
using?  Also, what boot proms?

> 
> We have type 8mm video tape backup devices, neither supports anything
> other than a red and a green light, the green light turns on
> when the tape is correctly inserted, the red light tells you there
> is power connected. I find the Gigatape display more useful because
> I like knowing what the tape is doing, like is someone writing it?
> is it rewinding, has it stopped, specially since the drive locks up
> sometimes requiring a system reboot.
> 

Is the drive itself locked?  What happens if you just reset the tape
drive (this can be a bit difficult if you have the exabyte mounted
in a cabinet with other devices)?  There is a possibility that the
device driver is the culprit.

>> What do you plan to do?  Hire someone to watch the front panel of the
>> tape drive and hammer the control-c if the drive is nearly full?
> 
> Very funny

Was meant to be, actually - I seem to have forgotten the :-).

> I was trying to show that this info is very useful because
> it allows you to get the numbers right for systems dumps, you know exactly
> how much can be written, we got these numbers from the exabyte
> by using lots of dd's with different block sizes and waiting till the tape
> runs out, then backing off 10%. 

That sounds like a safe way to estimate tape sizes, and should work fine
unless you get a very bad tape with a lot of invalidated blocks.
But, you don't _need_ a front panel display for this - dd will tell you
how much data was written.

>> Furthermore, (at least on the exabyte), all such statistics are available
>> with SCSI inquiry commands.  Much better to grab error stats and log
>> them than depend on users noticing the front panel display.
>> 
> 
> I prefer instant feedback, we differ, I also run my terminal with
> echo turned on.
> 

Personally, I prefer 5-bit with half duplex... :-).

The reason I prefer log files for this is that (at least at our site),
we usually don't have someone watching the tape drive during the backup
(or at any other time).  Log files permit later perusal of problem
conditions.

For instant feedback, just log stuff to the system console.

>> Who cares how fast a drive rewinds?
> 
> I care, I happen to search through tapes made up of lots of files
> and I much prefer a system that allows me to stick the tape in
> step many files to the end and take a look at the data contained
> in a matter of seconds [...]

I stand corrected here.  It is undoubtedly true that if you need to
search for files, the DAT drive will perform better.

> 
> Actually you are saying it takes 18 minutes to get to the last tape
> file so that you can search it to see if it is on that tape,
> if it isn't you need to load another tape which will take several minutes
> to rewind and unload, then you have to load a new tape.
> We cannot afford to keep a table of contents of the dumps on line, 
> so we have to make some guesses based on the last change time of the file
> to be restored.

I think the moral of the story here is that our needs and resources are
different.  We're backing up 4+ GB every friday, and we keep full logfiles
online at all times, so we don't need to guess where a file is located.
Our application requires high-speed read/write with high density, whereas
yours seems to require fast access to saveset "n" on the tape.

Being able to restore any file from a 2.3 GB tape within 20 minutes is
very acceptable at this site.

> I have lost big with these tapes before, many times, all info on later
> tape files was also lost. The DAT tape works for seeks to later files I
> know, I scratched the early part of a tape to test it.

I guess experience differs here too.  We've been using exabytes extensively
for quite a while without a read failure of any sort.  The only tape problems
we experienced was with a bad box of TDK tapes, and these were usable -
but could not record as much data (error correction kicked in a lot).  Sony
tapes have never given us a problem.
-- 
"Norf gribble mitz der bork bork bork?"        Roe Peterson
"Lick spittle dwing dtz fritz slppp!"          roe@sobeco.com
	- Uncle Duke                           uunet!sobeco!roe