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Subject: Re: [linux-lvm] balooning/dynamic snapshots?
From: "Brian J. Murrell" <brian@interlinx.bc.ca>
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Date: Tue, 13 Nov 2007 15:27:21 -0500
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To: LVM general discussion and development <linux-lvm@redhat.com>

On Tue, 2007-11-13 at 18:13 +0100, Tomasz Chmielewski wrote:
> 
> Is it possible to make a "balooning", or dynamic LVM snapshot? That is, 
> if the snapshot reaches its maximum, it will be automatically resized, 
> provided we still have space on the medium.

Yeah, that is something I wanted at one time.  In it's absence, I hacked
up the following brute-force solution.  I don't like the concept, but it
works.

        #!/usr/bin/ruby
        
        threshold=80.0
        increase_factor=0.5
        
        IO.popen("/testsuite/ltest-boulder/acceptance/common/timed_run 10 /usr/sbin/lvs") do |f|
          f.each_line do |line|
            j,volume,j,j,size,j,used = line.chomp.split(/\s+/)
            if used.to_f > threshold then
              # by bytes
              #size = eval(size.sub(/G$/, ' * 1024 * 1024 * 1024'))
              re = /([\d\.]+)([GM])/
              md = re.match(size)
              size = md[1]
              units = md[2]
              expand_by = size.to_f * increase_factor
              system("echo \"lv #{volume} was #{size}#{units} big and #{used} full and was expaned +#{expand_by}#{units}\" | mail -s \"snap expanded\" root")
              system("/testsuite/ltest-boulder/acceptance/common/timed_run 60 /usr/sbin/lvextend -L+#{expand_by}#{units} /dev/vg0/#{volume}")
            end
          end
        end

Put it in cron and run at an appropriate frequency.

b.