RE: Is My Data DESTROYED?!

["Guy Watkins" <linux-raid@watkins-home.com>]

} -----Original Message-----
} From: linux-raid-owner@vger.kernel.org [mailto:linux-raid-
} owner@vger.kernel.org] On Behalf Of Thomas Fjellstrom
} Sent: Sunday, October 25, 2009 1:26 AM
} To: linux-raid@vger.kernel.org
} Subject: Re: Is My Data DESTROYED?!
} 
} On Sat October 24 2009, Leslie Rhorer wrote:
} > > On Sat, Oct 24, 2009 at 6:52 PM, Leslie Rhorer <lrhorer@satx.rr.com>
} > >
} > > wrote:
} > > >> I'm going to go on a limb here and say for anyone (with data they
} want
} > > >> to preserve), no matter what, backups make sense and are cost
} > > >> effective. I'm going to be crazy and say that there's no reason
} that
} > > >> someone who thinks they can afford a 8TB disk array and dual SLI
} video
} > > >> cards, etc, etc, can't also consider some sort of disk or tape
} backup.
} > > >
} > > >        I agree with the disk backup, but not the tape.
} > > >
} > > >> Cumbersome? Can be. But having worked with datasets and filesystems
} > > >
} > > >        Cumberesome, slow, kludgy, and expensive.
} > >
} > > Well, like anything else, having a system helps. And by system I mean
} > > a library, barcodes on all tapes, and a good tape storage system. Yes,
} > > it involves Humans.
} >
} > 	Well, that wasn't quite my point, but it is another aspect of the
} > issue.
} >
} > > >> that run into the hundreds of terabytes, and having backed them up
} to
} > > >> tape, it makes sense. If you have something on the order of tens of
} > > >> disks, sure, go ahead, take that next step and back them up
} somewhere
} > > >> else to another set of disks. If you have more disks, seriously
} > > >> consider tape--in terms of capacity and power consumption (and data
} > > >> integrity), tape wins.
} > > >
} > > >        Power consumption, yes.  Capacity is a somewhat more complex
} > > > problem, with a number of variables.  For speed, tapes lose
} > >
} > > disastrously.
} > >
} > > > For cost, hard drives win unless the array is very large.  For
} > >
} > > reliability
} > >
} > > > and availability, drives win hands down.  I've had quite a bit of
} data
} > >
} > > lost
} > >
} > > > with bad tape sets, and the most persistent problems on my systems
} > > > which
} > >
} > > do
} > >
} > > > use tapes involve the tape drives, even sans data loss.  Once
} someone
} > >
} > > wiped
} > >
} > > > out a directory which someone up in corporate was backing up to
} tape.
} > >
} > >  It
} > >
} > > > took 3 days to recover the directory, no doubt because no one could
} > > > find
} > >
} > > the
} > >
} > > > tape.
} > >
} > > I'm not so sure about the speed--you can stream 100MB/sec to a single
} > > tape drive, and if you have multiple in a library, it just scales
} > > horizontally.
} >
} > 	First of all, that assumes the tape is loaded and ready.  It can
} > take hours or even days to retrieve a tape and load it.  Secondly, while
} >  the tape can stream 100MB/sec, it isn't random access.  Finding a 200
} byte
} >  file in the middle of a 1T tape backup is going to take a while.
} Getting
} >  it from an online backup server takes perhaps 10ms after the admin
} >  finishes typing the copy command.
} 
} Wouldn't you use some 'tar' like format on the tape so there's a file
} index
} you can search without having to scan the entire tape? Then you can just
} "ffwd" (seek) to the position. _should_ be lots faster than reading all of
} the
} data from the beginning to the files location trying to find it. Or maybe
} there's something I'm missing about tapes?

tar does not have an index.  The file name comes just before the file.  I
use cpio and gzip.  But I write to a USB disk.  I have restored 1 file, and
it had to scan through the data to find the file.

But back to your point.  I don't know of any open source software that can
restore a file quickly from tape.  And with a disk backup, if you use a file
system you can restore quickly.  But a file system wastes space.  That is
why I use cpio and gzip.  I backup about 500GB to a file about 350GB.  But
it really depends on how well your data compresses.

} 
} > > But, where I was working, we were also duplicating tape sets for
} > > offsite, which means there was two copies per backup set.
} > >
} > > Is this expensive? You betcha! But...you know. The bad old days of DDS
} > > are also gone, so there's some rejoicing there.
} >
} > 	They may be for you.  I have to manage over 300 of the beasts on the
} > same number of hosts.  What's worse, not only are the backups themselves
} > often incompatible, the drives often can't even use the same tapes.  I
} have
} > to see to it a half dozen different tape types get stocked in 75
} different
} > cities.  Then I have to try to make sure the gopher in every city
} remembers
} > to replace the tape.
} 
} :(
} 
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} 
} 
} --
} Thomas Fjellstrom
} tfjellstrom@shaw.ca
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