Adam Goryachev wrote at about 14:14:49 +1000 on Tuesday, September 1, 2009:
> Jeffrey J. Kosowsky wrote:
> > Jim Leonard wrote at about 20:20:59 -0500 on Monday, August 31, 2009:
> > > Jeffrey J. Kosowsky wrote:
> > > > Is it self-evident that a BackupPC tree is difficult to
> > > > copy/move/resize if not on a dedicated filesystem?
> > >
> > > What is a "dedicated filesystem"? How does it differ from any other
> > > filesystem?
> >
> > I mean a filesystem used just for a BackupPC topdir vs. a filesystem
> > that may contain data and/or code for multiple applications. Based
> > upon the nearly weekly postings on this group, it seems that many
> > people (myself included) initially set up their BackupPC topdir on a
> > filesystem containing mixed data and without the advantage of things
> > like LVM or ZFS since they don't realize in advance how hard it is to
> > copy/move/resize the topdir area due to the large number of
> > hard-links. It seems to me that new users should be strongly advised
> > to create topdir on a separate ("dedicated") filesystem on top of LVM,
> > ZFS, RAID, etc. to maximize flexibility. Alternatively, we can
> > continue to address this same issue every week ;)
>
> BTW, my "simple" solution to this apparently "major" problem was as follows:
> 1) Start using backuppc with a single FS (/) formatted with reiserfs (my
> preference).
As I mentioned this is not (well) documented in the BackupPC
documentation and continues to trip up new and not-so-new users
alike. Also, there are use cases where you can't have a single FS for
BackupPC (though Michael Stowe has decided to call them "fringe")
> 2) Backuppc grows too big for the FS, and I want to add RAID1 backup of
> the system
> 3) Purchase and install 2 x 1TB HDD's and configure with a single
> partition and use MD for RAID1
May be nothing for an enterprise but could be an issue for SOHO use. I
for instance don't have two empty 1TB drives and enclosures hanging
around.
> 4) Boot from CD/USB live linux system, and use dd to copy the old
> /dev/sda to /dev/md0
> 5) Adjust the /etc/fstab on the root FS to mount /dev/md0 onto
> /var/lib/backuppc
> 6) mount /dev/md0 somewhere
> 7) mv var/lib/backuppc backuppc
> 8) rm -rf all directories other than backuppc
> 9) mv backuppc/* .
> 10) rmdir backuppc
> 11) umount md0
> 12) adjust the partition size
> 13) adjust the filesystem size
> 14) reboot and enjoy the newly expanded pool size
>
> I really don't see why people think this is so difficult... Sure, there
> are lots of hardlinks, but block level copies are... simple. Sure, the
> new drive is bigger, but increasing partition sizes and filesystem sizes
> is simple. No "dangerous" operations, nothing technically hard or
> difficult... just simple standard unix tools to solve a problem by
> breaking it down into simple steps.
Some of those operations can be dangerous. I have made mistakes when
manipulating raid and filesystem sizes. But maybe I'm just sloppier
than most ;)
>
> I don't use LVM, in fact I don't really know how to use it. It might
> have made my life simpler if I had used it, but since I understand MD
> much more than I understand LVM, I find it more reliable for me.
The point is that playing around with mdadm, lvresize,
resize2fs/resize_rieserfs etc. are not everyday operations for me
and hence open to error - especially since the consequences of errors
can wipe out a whole fs or even disk. I don't think there is anything
wrong with expecting a program that is file-based to be copyable using
standard file-based tools. Sure you can make a setup that avoids the
problem by using dedicated filesystems and block-copying but that
doesn't seem ideal or natural. Again, nobody said there weren't any
solutions -- people just continue on a weekly basis to be dissatisfied
with them....
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