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*SOLVED* disk io with vzdump / vzmigrate [message #13276]

Thu, 24 May 2007 07:07

goeldi
Messages: 92
Registered: June 2006

Member

When I make a vzdump or vzmigrate using the suspend or the online feature (which is very cool!) disk IO goes very high. It goes so high that the system is no more usable (average load more than 20!). This is a system with about 20GB of data to sync/dump.

For the suspend or online option, rsync is used. In rsync is an option --bwlimit (bandwidthlimit) which limits not only network bandwidth but disk io bandwidth too.

It would be cool to see an option like the --ssh option in vzmigrate to give it some rsync options. Or is there another way for this?

[Updated on: Fri, 01 June 2007 07:11] by Moderator

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Re: disk io with vzdump / vzmigrate [message #13282 is a reply to message #13276]

Thu, 24 May 2007 08:16

rickb
Messages: 368
Registered: October 2006

Senior Member

Linux itself has no way to do what you want (limit disk i/o bandwidth per process). However, the 2.6.18+ cfq scheduler supports i/o priorities, check out ionice and set the migrate pid to a low priority or the idle class.

Quote:

[root@arsenic ~]# /root/bin/ionice -h
Usage: ionice [OPTIONS] [COMMAND [ARG]...]
Sets or gets process io scheduling class and priority.

-n Class data (typically 0-7, lower being higher prio)
-c Scheduling class
1: realtime, 2: best-effort, 3: idle
-p Process pid
-h This help page

Jens Axboe <axboe@suse.de> (C) 2005

your disk i/o could be full, however you will not feel it as all other processes have significant priority. the vz tools do not set io priority yet directly, however you can re-ionice the process after it has been started.

good question!

-------------
Common Terms I post with: http://wiki.openvz.org/Category:Definitions

UBC. Learn it, love it, live it: http://wiki.openvz.org/Proc/user_beancounters

[Updated on: Thu, 24 May 2007 08:33]

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Re: disk io with vzdump / vzmigrate [message #13379 is a reply to message #13276]

Fri, 25 May 2007 11:20

Vasily Tarasov
Messages: 1345
Registered: January 2006

Senior Member

Hello,

I want to ask you some questions:

1. Kernel you're using

2. You write "disk IO goes very high". Can you be more precise? Please, post tools output and other appropriate stuff.

3. You write "...the system is no more usable". What do you mean? The response of the system is very long? Can you give some certain examples?

4. You write "average load more than 20!". Sorry for my ignorance, where do you get this digit (20) and what it means? Wink

Thank you,
Vasily.

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Re: disk io with vzdump / vzmigrate [message #13383 is a reply to message #13379]

Fri, 25 May 2007 12:03

goeldi
Messages: 92
Registered: June 2006

Member

Vasily Tarasov wrote on Fri, 25 May 2007 07:20

Hello,

I want to ask you some questions:

1. Kernel you're using

2.6.18-ovz028stab031.1-smp

Quote:

2. You write "disk IO goes very high". Can you be more precise? Please, post tools output and other appropriate stuff.

This was only my interpretation.

Quote:

3. You write "...the system is no more usable". What do you mean? The response of the system is very long? Can you give some certain examples?

Last night I made a vzdump of about 10GB in 6 VEs. Average system load (see it with command w or with top) went to over 50.0 for about 2 hours. I hid Ctrl-C and it took about half an hour to stop vzdump.

Quote:

4. You write "average load more than 20!". Sorry for my ignorance, where do you get this digit (20) and what it means? Wink

output of top or w
I see it in a gkrellm client too.

At the same time, cpu usage is about 0% - 1%

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Re: disk io with vzdump / vzmigrate [message #13386 is a reply to message #13383]

Fri, 25 May 2007 12:16

Vasily Tarasov
Messages: 1345
Registered: January 2006

Senior Member

There was quite a big bug in disk I/O that causes high I/O load in our tests and it was fixed only in 032 kernel. Can you please try to apply this patch http://git.openvz.org/?p=linux-2.6.18-openvz;a=commit;h=c7fa 58b331d23c0796996dcab75c72053fafab5a
and then inform us, does it help?

Thank you,
Vasily.

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Re: disk io with vzdump / vzmigrate [message #13512 is a reply to message #13282]

Tue, 29 May 2007 06:30

goeldi
Messages: 92
Registered: June 2006

Member

I cannot find ionice tool anywhere. Where do i get it?

Does you comment mean, that I may upgrade to kernel 2.6.20 to get this option?

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Re: disk io with vzdump / vzmigrate [message #13513 is a reply to message #13386]

Tue, 29 May 2007 06:37

goeldi
Messages: 92
Registered: June 2006

Member

this is a productive system. I would prefer not to apply patches to the kernel[/coward]

BTW: Last night I tried to start rsync as a daemon on the target system with option --bwlimit=100, but now I have another problem ( http://forum.openvz.org/index.php?t=tree&goto=13511& #msg_13511).

Would it be a possibility to start a bwlimited rsyncd on the target system? Does vzmigrate take notice of a rsync daemon?

And another question: I tried to first make a normal bwlimited rsync from source to target system. I made this because I thought that after that vzmigrate would sync only the changes. But obviously vzmigrate always transfers everything, because it ended with the error message, that the target directory already exists Sad

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Re: disk io with vzdump / vzmigrate [message #13517 is a reply to message #13512]

Tue, 29 May 2007 07:10

curx
Messages: 739
Registered: February 2006
Location: Nürnberg, Germany

Senior Member

> I cannot find ionice tool anywhere. Where do i get it?

it's in package "schedutils"

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Re: disk io with vzdump / vzmigrate [message #13519 is a reply to message #13517]

Tue, 29 May 2007 07:30

goeldi
Messages: 92
Registered: June 2006

Member

In schedutils I have 2 tools: chrt and taskset. So if I do this while vzmigrating:

chrt -p 99 <pid>

where <pid> is the pid of the rsync process, rsync on the target side will get a priority of 99?

Can you suggest me, where I get more USER information for priorities? Is it comparable with nice (highnumber=slow, lownumber=fast) and what is the highest/lowest priority I can give?

Sorry for these newbie questions, but nobody else seems to ask this :-/

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Re: disk io with vzdump / vzmigrate [message #13527 is a reply to message #13519]

Tue, 29 May 2007 10:31

Vasily Tarasov
Messages: 1345
Registered: January 2006

Senior Member

If you have linux sources read about ionice tool in Documentation/block/ioprio.txt file.

HTH,
Vasily.

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Re: disk io with vzdump / vzmigrate [message #13649 is a reply to message #13513]

Fri, 01 June 2007 07:10

Vasily Tarasov
Messages: 1345
Registered: January 2006

Senior Member

I close this thread as *SOLVED*, since initial problem is solved in 033 kernel (look at http://bugzilla.openvz.org/show_bug.cgi?id=602)

If you have other problems - please - post them as a separate thread.

Thank you,
Vasily.

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