On 11/23/2014 04:59 AM, Nipun Arora wrote:
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)
Please retry with vzctl 4.8 and ploop 1.12.1 (make sure they are on both
sides).
There was a 5 second wait for the remote side to finish syncing
copied ploop data. It helped a case with not much I/O activity in
container, but
ruined the case you are talking about.
Newer ploop and vzctl implement a feedback channel for ploop copy that
eliminates
that wait time.
http://git.openvz.org/?p=ploop;a=commit;h=20d754c91079165b
http://git.openvz.org/?p=vzctl;a=commit;h=374b759dec45255d4
There are some other major improvements as well, such as async send for
ploop.
http://git.openvz.org/?p=ploop;a=commit;h=a55e26e9606e0b
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?
You can create a ploop snapshot and use shared base image for both
containers
(instead of copying the base delta, hardlink it). This is not supported
by tools
(for example, since base delta is now shared you can't merge down to it,
but the
tools are not aware) so you need to figure it out by yourself and be
accurate
but it should work.
Thanks
Nipun
On Sun, Nov 23, 2014 at 12:56 AM, Kir Kolyshkin <k...@openvz.org
<mailto:k...@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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