[Users] Live Migration Optimal execution

[Nipun Arora]

Hi Kir,

Thanks for the response, I'll update it, and tell you about the results.

1. A follow up question... I found that the write I/O speed of 500-1Mbps
increased the suspend time  to several minutes.(mostly pcopy stage)
This seems extremely high for a relatively low I/O workload, which is why I
was wondering if there are any special things I need to take care of.
(I ran fio (flexible i/o writer) with fixed throughput while doing live
migration)

2. For my purposes, I have modified the live migration script to allow me
to do cloning... i.e. I start both the containers instead of deleting the
original. I need to do this "cloning" from time to time for the same target
container...

       a. Which means that lets say we cloned container C1 to container C2,
and let both execute at time t0, this works with no apparent loss of
service.

        b. Now at time t1 I would like to again clone C1 to C2, and would
like to optimize the rsync process as most of the ploop file for C1 and C2
should still be the same (i.e. less time to sync). Can anyone suggest what
would be the best way to realize the second point?


Thanks
Nipun

On Sun, Nov 23, 2014 at 12:56 AM, Kir Kolyshkin <kir at openvz.org> wrote:

>
> On 11/22/2014 09:09 AM, Nipun Arora wrote:
>
> Hi All,
>
>  I was wondering if anyone can suggest what is the most optimal way to do
> the following
>
>  1. Can anyone clarify if ploop is the best layout for minimum suspend
> time during live migration?
>
>
> Yes (due to ploop copy which only copies the modified blocks).
>
>
>  2. I tried migrating a ploop device where I increased the --diskspace to
> 5G,
> and found that the suspend time taken by live migration increased to 57
> seconds
> (mainly undump and restore increased)...
> whereas a 2G diskspace was taking 2-3 seconds suspend time... Is this
> expected?
>
>
> No. Undump and restore times depends mostly on amount of RAM used by a
> container.
>
> Having said that, live migration stages influence each other, although
> it's less so
> in the latest vzctl release (I won't go into details here if you allow me
> -- just make sure
> you test with vzctl 4.8).
>
>
>  3. I tried running a write intensive workload, and found that beyond
> 100-150Kbps,
> the suspend time during live migration rapidly increased? Is this an
> expected trend?
>
>
> Sure. With increased writing speed, the amount of data that needs to be
> copied after CT
> is suspended increases.
>
>
>  I am using vzctl 4.7, and ploop 1.11 in centos 6.5
>
>
> You need to update vzctl and ploop and rerun your tests, there should be
> some improvement (in particular with respect to issue #3).
>
>
>  Thanks
> Nipun
>
>
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