Regarding tapes: this is one of the advantages of using HSM and physical
tapes. It's quite easy to manage that even very old backup is on quite
recently recorded tape. Migration from older tape system to new one is
piece of cake. For VTS things are a bit more complex but still it is
possible. "Fresh" tapes are better than 15-years old cart, last mounted
10 years ago. Not to mention weared drives.
And of course always use two physical tapes. Preferrably in two
locations. Even the best tape may fail. Two cart also may fail, but it
is less likely. Three tapes (in three ATLs, in three locations) are even
more unlikely to fail concurrently, etc. And it is your decision to say
"n copies is enough safety for me". And I'm sorry, I don't believe in
any support from business side.
BTW: two tapes, but avoid to write or read them in same drive. Drive
failure may somehow destroy the tape. I know a guy who tried to recover
data from backup, but the tape was faulty. He had two copies. Second
reel was also faulty. Actually both tapes were mounted in same faulty
drive which destroyed both copies. In that scenario even dozen of copies
would not help (assuming still same drive).
--
Radoslaw Skorupka
Lodz, Poland
W dniu 08.07.2020 o 16:07, Vernooij, Kees (ITOP NM) - KLM pisze:
I agree with your findings.
At one time, one headlight of my car failed. Since it has two headlights, I did
not make much hurry to replace it, but 2 days later the other one failed. Then
I was left in almost complete darkness. A SPOF is a SPOF and is subject to
Murphy's law, which means it will hit you at the most inconvenient momemt.
The TS7740 has several selection criteria for physical tape reclaims: one is
the period a tape has not been mounted. The max period you can set here was 365
days (or not do it at all). There must be a good reason to limit this period to
1 year, not more.
Kees.
-----Original Message-----
From: IBM Mainframe Discussion List <IBM-MAIN@LISTSERV.UA.EDU> On Behalf Of
Bill Ogden
Sent: 08 July 2020 15:27
To: IBM-MAIN@LISTSERV.UA.EDU
Subject: Re: Storage & tape question
Probably many others will chime in on this. I have lost RAID 5 arrays with
two disk failures within an hour of each other. RAID is nice, but one must
allow for failures.
Long ago I was involved with reading archived tapes and transferring the
data to CDs. The programs involved were home-written and the project ended
up going nowhere. However, we discovered that tapes kept too long started
having errors. (At that point, for the CD copy, we just logged the error
and accepted the corrupt data; what else could we do?) How long is "too
long"?? It was variable, but measured in a few years. The advice then was
to minimally read the tapes every year or so to "retension" them. Don't
know if this would apply to more modern tape media. (We also discovered
that locally "burned" CDs are not expected last forever.)
IMHO, the key point for tape backups are (1) off-site storage, (2)
multiple PiT recovery, (3) logical error recovery. All this can be done
with disk-only environments involving remote copy and lots of disk space,
but all that becomes expensive for smaller shops.
Bill Ogden
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