On 11/23/2014 07:13 PM, Nipun Arora wrote:
Thanks, I will try your suggestions, and get back to you.
btw... any idea what could be used to share the base image on both
containers?
Like hardlink it in what way? Once both containers start, won't they
have to write to different locations?
ploop is composed as a set of stacked images, with all of them but the
top one being read-only.
I understand that some file systems have a copy on write mechanism,
where after a snapshot all future writes are written to a additional
linked disks.
Does ploop operate in a similar way?
yes
http://wiki.qemu.org/Features/Snapshots
http://openvz.livejournal.com/44508.html
The cloning with a modified vzmigrate script helps.
- Nipun
On Sun, Nov 23, 2014 at 5:29 PM, Kir Kolyshkin <k...@openvz.org
<mailto:k...@openvz.org>> wrote:
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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