1,000,000 passes < at > 512 per week is about 37 years. If I remember right
an LTO4 is a 256 track serpentine tape, two complete writes per week is
512 passes. We do not have many tapes that are fully written twice per
week. Shoe shining is only going to double the passes for that section
of tape for that write, so maybe we get it down to 17 years for parts of
the tape. I hope to change tape technology before I reach 17 years.
Or 1 full pass every week plus one extra pass every 11 days is about 42
years.
Andy Huebner
-----Original Message-----
From: ADSM: Dist Stor Manager [mailto:ADSM-L < at > VM.MARIST.EDU] On Behalf Of
Roger Deschner
Sent: Tuesday, August 12, 2008 10:33 AM
To: ADSM-L < at > VM.MARIST.EDU
Subject: Re: [ADSM-L] FW: [ADSM-L] Reclamation Tape Count...
Beware that the figure of several million passes, quoted by
manufacturers, is misleading. An average single write-cycle of one tape
(i.e. a single time filling it from empty to full via migration and/or
reclamation) can involve hundreds of so-called "write-passes" - even if
it's only mounted once to migrate something huge, and is not subjected
to "shoeshining". Mount it many times to migrate small sets of data, and
then add a few restores, and those passes add up very quickly. Therefore
you can burn through your millions in a hurry, even with LTO4's "write
slowly" technology that greatly reduces shoeshining.
Worse, a tape that actually does shoeshine can wear out its millions of
passes in very short order. I suspect that nearly all tape-to-tape
reclamation shoeshines to some extent, as the output tape waits for TSM
to find the next file it wants to keep on the 50%-empty input tape.
Perhaps somebody smarter than me can figure out a way to measure
shoeshining, or how many "passes" a tape has had, but I don't think the
data exists. My suspicion is that if you could accurately count
"passes", we'd find that tapes actually last quite a bit longer than the
manufacturer's specs.
Due to drastic differences in the number of uses of a particular tape
over a period of time (say, a year), it's useless to use elapsed time as
a measure of how worn a tape is. We have very active and very slow
management classes, depending on the volatility of the actual data. The
tapes unlucky enough to be picked for a volatile type of data (email...)
get beat up pretty fast, while those lucky enough to go on long-term
vacation storing archive data will last forever. You also have to count
restores.
Also, I think one of the most important factors in predicting tape life
is how many times it is removed from the library and transported. This
subjects it to temperature and humidity changes, dust, electromagnetic
fields, mechanical shock, and who knows what other hazards of the
outside world. Tapes that stay locked inside a library in a
climate-controlled computer room will last considerably longer.
We track all errors via AIX erept and by mechanically scanning the TSM
activity log. I gave up on using status=private volumes, because the
long-term statistics it collects are of limited use, and have gone back
to plain scratch tapes which are much easier to manage. We do not count
errors against a tape volume which were obviously the drive's fault. A
tape is retired on its SECOND media error. Since we got our new library
with LTO4 technology in January 2008, we have had 0 (zero) tapes retired
for any reason, including media faults. Our only LTO4 tape faults of any
kind have been unload failures.
There's quite a bit of hocus-pocus here, about technology that is really
extremely reliable. Some of it is basically urban legend remembered from
9-track open-reel IBM 3420 days. The ultimate answer is of course 42.
http://en.wikipedia.org/wiki/Answer_to_Life,_the_Universe,_and_Everythin
g
Roger Deschner University of Illinois at Chicago rogerd < at > uic.edu
======I have not lost my mind -- it is backed up on tape somewhere.=====
TSM does not keep information on a tape beyond its current use.
Not sure about LTO, but they are similar to 3590 which we run to the
first write error. In general this takes years, but I have no idea how
many mounts.
Andy Huebner
-----Original Message-----
From: ADSM: Dist Stor Manager [mailto:ADSM-L < at > VM.MARIST.EDU] On Behalf
Of
M.Kiran Kumar
Sent: Friday, August 08, 2008 12:54 AM
To: ADSM-L < at > VM.MARIST.EDU
Subject: [ADSM-L] Reclamation Tape Count...
Hi,
Please let me know how to check the tape, how many times it is
reclaimed
in
TSM. And how many times can we use a LTO Gen3 and LTO Gen4 Media??
Regards,
Kiran M
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