[Coco] LSN0 C code

[gene heskett]

On Saturday, June 11, 2011 01:20:25 PM Steven Hirsch did opine:

> On Sat, 11 Jun 2011, gene heskett wrote:
> > Yes, I've managed to wipe out both a DDS-2, and a couple of Travan
> > cartridges before I discovered that.  For both, I was trying to
> > disable the drives compression flag, which once turned on, cannot
> > generally be turned off by any normal drive command.
> > 
> > I found the secret is to use dd to read the first 32k block out to a
> > file, rewind the tape, issue the compress off command without giving
> > the drive a chance to re-read the header, then, again using dd,
> > rewrite that label header, which will force most drives to update
> > that (&^$#@) flag to off. GZip can very easily beat the drives
> > compression ratio, and since amanda counts bytes sent down the cable,
> > it knows how much it was written to that tape.  I when tape limited,
> > routinely filled a tape to 98% without every hitting the EOT signal. 
> > Now I use a big hard drive as 30 virtual tapes and don't worry about
> > it.
> 
> I'll file that trick away for posterity - thanks.  This is getting
> off-topic, but I am surprised that you trust rotating media for archival
> backup.  I'm a big believer in belt+suspenders.  All my working machines
> have RAID arrays (one software RAID and the other a 3ware smart
> controller) and LTO2 tape drives.  I use a rotating sequence of LTO
> tapes.

Well, so far I have been through 3 drives in that position, in about 6 
years time, and about 4 drives in the boot from it position, which may or 
may not be the first drive.  Each one gracefully approached its end of life 
in a manner (smartd monitoring basically) that gave me time to run up the 
interstate, get another drive, plug it in and do an rsync with the only 
data losses being my own fault because that particular item got caught by a 
wild card exclude command.

What we need, and do not have, is a method of reading the system and 
comparing it to the backups, so as to list what is missing and may be 
potentially valuable.

We use raids at the tv station, but the track record there doesn't seem to 
confirm any enhanced dependability.  Drive failures there are just as 
deadly if two fail at the same time.  And there has been 3 or 4 occasions 
where identical drives also failed at nearly identical times.

Cheers, gene
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