Re: [BackupPC-users] How do I use an external USB drive as backup target?

[John H. <jj...@gm...>]

my comments are interspersed below...

On Sat, Feb 13, 2010 at 6:40 PM, Jeffrey J. Kosowsky
<bac...@ko...>wrote:

> John Hudak wrote at about 12:06:29 -0500 on Saturday, February 13, 2010:
>  > Hello:
>  > I am considering using an external USB drive as the storage for my
> backups.
>  > I am running backup pc under Debian 5.0.
> External USB drives are a *BAD* idea for multiple reasons:
> - Slow
> - Unreliable
> - Subject to being disconnected
> etc.
>
> Yes, I know 1, and 2 is 'it depends', and 3 is exactly the reason why I
want to use usb drives


>  > Part 1
>  > What do I need to do to configure the USB disk as the target? (e.g. how
> do I
>  > do it?)
>  > The USB disk is currently formatted as a NTFS file system.  Do I *need*
> to
>  > reformat it to ext3? or other?
> - NTFS is not usually used - need to check whether it supports the
> types of hard links required for BackupPC
>
>  >
>  > Part 2
>  > Assume I am crazy paranoid about preserving backup data and I get a
> second
>  > USB drive to serve as a backup to the first USB drive.
>  > Also assume that I am not concerned about the bandwidth across the
> network
>  > or the various buses.
>  >
>  > >From a data reliability standpoint, is it better to run a backup
> session to
>  > USB drive 1, and then repeat the backup to USB drive 2? OR
>  > run a backup session to USB drive 1, and then copy the backup
> directories to
>  > USB drive 2???
> Look at the archives and FAQ - this has been discussed *many* times so
> no point in wasting peoples time in rehashing.
>
> I did a quick search of the archives before asking - I did not find a
definitive answer...


>  > The first approach could have errors in different backed up files on
> disk 1
>  > or 2 but given the odds, very unlikely that the same exact error would
> show
>  > up
>  > in the same exact way in the same file across both USB disks.
>  > OTOH, the second approach would allow the exact error in the backup on
> USB
>  > disk 1 to be copied to USB disk 2.
>  >
>  > I am leaning towards repeating the backup on two drives.
>  >
>  > My understanding is that files that are backed up (using either rsync or
>  > smb) are 'encrypted' (for lack of a better word), and to view them I
> need to
>  > use zcat.-True?
>
> There is a better word -- *compressed*
>
So that is the word that is not clearly used in the documentation.  There
are many ways that backups can be manipulated: stored in a completely
nonstandard/proprietary file system and protocol such as z-san, they can be
encrypted, and they can be compressed.  The backup PC doc talks about using
compression, but does not state if any compression is used in the default
configuration.  Compression is often configuration parameter.  It does not
make sense to compress many audio and video formats.  If the data to be
backed up consists predominantly of these types of files, then it makes no
sense to waste CPU cycles applying compression to get < 5% compression.


>  > Also, can the backup profile be specified to perform complete data
> copies
>  > periodically, as opposed to a baseline and then periodic incrementals?
>
> Read the documentation and FAQ.
>
I have read the doc, (where IMHO) this should have been clearly stated.
Instead the doc frequently introduces a topic with 1-2 sentences, then goes
off on a tangent for 1-3 paragraphs about how things were done in a previous
verson (completely irrevelant), or talks about what will be comming (again,
irrelevant), or points one to another section of the doc, in the middle of
some other thread that is related to the topic but does not address the
topic at hand, or,  introduces a topic, then talks about 3-4 other ways to
accomplish the same thing, without telling the reader exactly how to do the
initial topic to begin with.  So my fault...I need to also read FAQs.

>
>  > Lastly, does anyone have a statistical number that represents the
>  > probability of a backup file (e.g. on the target backup disk) containing
> an
>  > error introduced
>  > by the backup procedure?  I know there are error probabilities for both
> disk
>  > and tape reads/writes failures, but am wondering if anything like that
>  > exists for the backup software.  (A group I used to work with did this
> sort
>  > of testing, and actually had some statistics on the reliability of
> backup
>  > programs, wrt types of files, sizes, w/wo compression, and the types of
>  > compression.   Not sure the open source community would go through this
> type
>  > of assessment - but thought I'd ask.
>
> The probability is either 0 if no bugs in the software (or your
> configuration of it) or 100% if bugs in the software and your dataset
> triggers the bug. Your question is not very well-framed and pretty
> meaningless. I suggest you learn a bit more about backup in general
> and backuppc in particular. There is a lot of good documentation on
> BackupPC in the Wikki and in the archives, I suggest you reference it...


Well, in the extremely simplistic and ideal case, it is 0 or 1.  In the real
world, where algorithms are badly designed, or implemented, or both, then
problems arise due to things not originally considered in the development
which cause errors to arise in the backup procedure that is not about the
conversion of 0/1's in computer memory or the transferring of them to tape,
disk, etc.
The question to you may be meaningless, but it is not to me, and it wasn't
to an R&D group that I worked in to look at this precise issue.
Again, the documentation (e.g. manual) for backup PC, leaves a lot to be
desired.  While I was reading through the  issues in the forum, it struck me
the number of times I came across the phrase "I followed the directions and
it did not work/having trouble," etc.   I guess I have to spend a lot of
time searching archives to find this info, and then figure out if it applies
to this version, or a previous version.
-J


>
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