more comments in line.
On 08/10/2016 03:31 PM, Steve Petrie, P.Eng. via talk wrote:
Hello Alvin,
Please see my comments inline below.
[snip]
On 4mm backups.
There was a customer who used a 4mm backup and backed up every night.
The one thing someone forgot to tell them was to replace the tapes.
After about 4 years the disk failed.
The tapes were transparent.
After the customer's nightly backup process wrote to the tape, was
there also a separate verify phase, that rewound and read through the
entire tape, and compared its contents with the HDD data?
Surely a verify phase would have failed with unreadable (transparent)
tapes. And failure of the verify phase, would have alerted the
customer to the unreadability problem with the tapes.
Verify phase.
You make me laugh.
HAHAHA.
I did not write the code if I did then there would likely have been a
verify phase.
Some people kind of expect when you tell the drive to write the data its
just written and if it were not there would be an error. Kind of like
disk drives most times.
Anyway.
When you do the verify you need to actually verify the data and not just
the block checksums.
Once upon a time a company I worked for had a bug that would write blank
tapes.
More correctly tapes full of zero filled blocks.
They checksumed correctly so the quick check would succeed but not restore.
Guess how this story ended?
The story ended very badly, no doubt. The cruel "nasty surprise"
downside, of our beautiful profession ...
They got back up and running and from that point forward the backups
were done properly.
Nothing like getting burned to teach you.
--
Alvin Starr || voice: (905)513-7688
Netvel Inc. || Cell: (416)806-0133
al...@netvel.net ||
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Netvel Inc. || Cell: (416)806-0133
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