[Coco] Possible CoCo Bulletin Board forum

[Gene Heskett]

On Thursday 25 December 2008, Steven Hirsch wrote:
>On Thu, 25 Dec 2008, Gene Heskett wrote:
>>> It's seriously difficult to kill data on a DLT cartridge.  I've
>>> personally seen cases where tapes run over a bulk eraser were still
>>> readable!  The drives use read-after-write to ensure integrity and will
>>> redo any blocks that fail CRC (up to a limit).  The lack of read-back is
>>> a serious issue for the rotary-head transports which are mechanically
>>> incapable of it (at least AFAIK).
>>
>> Bulk erasers don't have the cajones to erase a data or vieo tape unless it
>> says Garner on it.
>
>Ah.  Now I know what to look for!  I've been using an older Nortronics
>unit intended for reel-to-reel audio tape.  Whenever I have to wipe a data
>cartridge, I place a U-shaped piece of steel over the top to focus the
>flux lines.  Buzzes like a b*tch, but gets the job done :-).
>
>> Anyway, the virtual tapes, on a 500GB hard drive, are many times more
>> dependable, I've not lost a byte since.  And I don't worry about backups,
>> I have a user named amanda who runs herself evey morning at a little after
>> 1 and does all that without any interference from me.
>
>I would be very concerned about putting all my eggs in one basket like
>that.  My working theory on hard drives is that there are two types:
>
>Those that have failed already and those that are about to.

I tend to agree, but it has also been my experience that if one peruses the 
logs, you will see an error or 30 before they drop over.  I use that for a 
hint to get my butt to town and get another drive and copy it to the new 
drive, before the failure is total.  I have done that twice since 2001 when I 
switched.

>That's why data-retention experts recommend against using RAID for
>archival purposes, BTW.  Just because the chances of losing >1 drive in a
>RAID-5 array are infinitesmal does not mean it cannot happen.

Particularly if they are Velociraptors, one fellow on lkml has in the last 
month lost all 5 of them in his raid.

>I didn't realize that rotary head devices were capable of supporting
>read-after-write.  Thanks for the update!

With enough $$ thrown at the head, it can be done.  The dvc-pro also does this 
unless its doing an insert mode.  IIRC the normal record head is then the 
erase head because its track is a few microns narrower, and the confidence 
head actually writes the new data.  I think.

>Steve

-- 
Cheers, Gene
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
What orators lack in depth they make up in length.