[ClusterLabs] Antw: [EXT] Re: Problem with high load (IO)

[Strahil Nikolov]

These 'dirty' sysctl settings are configureable. For large sequential I/O it's desirable 'dirty' ratio/bytes to be bigger, while for small files/random I/O it's better to be kept low.

Best Regards,
Strahil Nikolov






В вторник, 5 октомври 2021 г., 08:52:20 ч. Гринуич+3, Ulrich Windl <ulrich.windl at rz.uni-regensburg.de> написа: 





>>> Gang He via Users <users at clusterlabs.org> schrieb am 30.09.2021 um 03:55
in
Nachricht <afb3d125-3573-a12f-406f-96724eaf154b at suse.com>:

> 
> On 2021/9/29 16:20, Lentes, Bernd wrote:
>> 
>> 
>> ‑‑‑‑‑ On Sep 29, 2021, at 4:37 AM, Gang He ghe at suse.com wrote:
>> 
>>> Hi Lentes,
>>>
>>> Thank for your feedback.
>>> I have some questions as below,
>>> 1) how to clone these VM images from each ocfs2 nodes via reflink?
>>> do you encounter any problems during this step?
>>> I want to say, this is a shared file system, you do not clone all VM
>>> images from each node, duplicated.
>>> 2) after the cloned VM images are created, how do you copy these VM
>>> images? copy to another backup file system, right?
>>> The problem usually happened during this step?
>>>
>>> Thanks
>>> Gang
>> 
>> 1) No problems during this step, the procedure just needs a few seconds.
>> reflink is a binary. See reflink ‑‑help
>> Yes, it is a cluster filesystem. I do the procedure just on one node,
>> so i don't have duplicates.
>> 
>> 2) just with "cp source destination" to a NAS.
>> Yes, the problems appear during this step.

> Ok, when you cp the cloned file to the NAS directory,
> the NAS directory should be another file system, right?
> During the copying process, the original VM running will be affected, 
> right?

One issue, especially with large RAM systems is this: If you copy from a fast
to a slow device, the RAM wil fil with dirty buffers, probably causing a read
starvation (no discardable buffer available). So this can affect any unlelated
process.
(Actually in the past it affected the IPaddr monitor for us)
However I think recent kernels (maybe it's SUSE specific) prevent the whole
free RAM to be filled with dirty buffers.

Regards,
Ulrich

> 
> Thanks
> Gang
> 
>> 
>> Bernd
>> 
> 
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