[Dirvish] Copying dirvish vaults (heavily hard linked)

Keith Lofstrom keithl at kl-ic.com
Thu Mar 6 18:28:31 UTC 2008


> On Thursday 06 March 2008 09:21:53 am Keith Lofstrom wrote:
...
> > See also the ancient:  http://wiki.dirvish.org/index.cgi?CopyingDisks

On Thu, Mar 06, 2008 at 09:33:52AM -0700, Shawn (Red Mop) wrote:
> Tar is actually very fast.  I used it to split a bank about a month ago.  It 
> was a little unnerving, so I ran rsync -aH on top of (after) tar, and rsync 
> did almost nothing.  The du -hcs * in each vault already matched.

"Almost nothing", unfortunately, can be a big difference.  When I was
testing, tar did not produce bootable images, because some of the special
files did not copy.   Perhaps it has been improved.  rsync does produce
bootable images (if it did not, then dirvish wouldn't be very useful).

My point is that these file copy tools can take a surprisingly long
time.  My 500GB backup drive is now about 70% full, with about 100
images on it (I do not expire them), meaning that to some tools, on
the file level, the drive appears to contain around 60 terabytes. 
A drive copy at the file level will attempt to traverse a large
fraction of that 60TB;  if the interface is running at 20MB/sec
that will take a large fraction of 800 hours.  Yikes!

> LVM + resize2fs is one of my very best friends.  I grow and shring partions 
> all the time.  It's a real kick to move a partition from one disk to another 
> while the partition is in use without rebooting, or even taking the partition 
> offline.

Yes, fine tools.  I wish resize2fs had an extra option for increasing
or decreasing inode *density*.  It does add or subtract inodes as you
grow or shrink partitions, maintaining the ratio of inodes to data,
but sometimes the problem is a lack or surplus of inodes.  "Plan
ahead" is not always possible or easy with heavily hard-linked file
systems with unpredictable future usage.  

Is there a tool that permits the manipulation of inode density on
a used file system?

Keith

-- 
Keith Lofstrom          keithl at keithl.com         Voice (503)-520-1993
KLIC --- Keith Lofstrom Integrated Circuits --- "Your Ideas in Silicon"
Design Contracting in Bipolar and CMOS - Analog, Digital, and Scan ICs


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