[linux-lvm] balooning/dynamic snapshots?

[linux-lvm] balooning/dynamic snapshots?

[Tomasz Chmielewski]

Right now, one has to specify a snapshot size.

If the snapshot takes more space that one specified with -s (size), that 
snapshot is automatically dropped, and is no longer usable.


Sometimes, it is just not possible to know beforehand how much data will 
change, but on the other hand, specifying 100% snapshot size is not 
possible or hard to estimate.


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.

Looking at lvm manuals, I didn't see such a feature, and the only 
possibility seems to be to create a userspace program which would check 
the status of the snapshots periodically, and resize them if needed - 
but this seems crude, and may not work sometimes (very loaded system, 
volumes with a lot of writes etc.).


-- 
Tomasz Chmielewski
http://lists.wpkg.org

Re: [linux-lvm] balooning/dynamic snapshots?

[Brian J. Murrell]

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.

Re: [linux-lvm] balooning/dynamic snapshots?

[Brian J. Murrell]

On Tue, 2007-11-13 at 15:27 -0500, Brian J. Murrell wrote:
>         
>         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}")

Ooops.  I should have mentioned
that /testsuite/ltest-boulder/acceptance/common/timed_run is simply a
wrapper that time-bounds a command.  You can disregard it's use at the
risk of an lv* command hanging and running forever.

b.

[linux-lvm] lvm library progress?

[ben scott]

I saw a recent reference on this list to the development  of a library for lvm 
functions. Is this at a point where it could be used for anything useful? I 
have written a program that calls the lvm programs directly but would prefer 
to use a library if possible. Even if only some functions are done that might 
still be helpful. 

Thank you.
Ben Scott
benscott@nwlink.com

Re: [linux-lvm] lvm library progress?

[Greg_Swift]

The python library I was working on has only gotten so far.  It does still
rely on the lvm commands, at this point *display gathers information. Due
to the lack of response from people here and my OCD oriented tendancies to
have it be "right" I've actually only ended up implementing very basic
functionality.  Right now you can gather information about a pv, vg, or lv.
You can run vgcfgbackup, and then you can restore a pv referencing that
file, and you can restore a vg and its lvs with the vgcfgrestore command.
It also imports data from an XML utility a co-worker wrote so that in a
restore environment you can populate the objects without being able to pull
their info from the system. (effectively pickling the data, but with xml).

The template for the other functions is there and easy to populate, and the
display function might need to be migrated from *display to *s.
Unfortunately I got little feed back so this is as far as I've gotten since
its all i have to have for the application I'm writing.  Long-term I'd like
to see a more complete module, but I would need a more detailed
understanding of LVM, imo, to do that.  And while I keep reading up, I
don't know how detailed of an understanding I will ever really have.

-greg

linux-lvm-bounces@redhat.com wrote on 11/25/2007 11:12:31 PM:

> I saw a recent reference on this list to the development  of a
> library for lvm
> functions. Is this at a point where it could be used for anything useful?
I
> have written a program that calls the lvm programs directly but would
prefer
> to use a library if possible. Even if only some functions are done that
might
> still be helpful.
>
> Thank you.
> Ben Scott
> benscott@nwlink.com
>
> _______________________________________________
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