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

[Ulrich Windl]

>>> Strahil Nikolov via Users <users at clusterlabs.org> schrieb am 05.10.2021 um
12:00 in Nachricht <997665166.1212448.1633428038216 at mail.yahoo.com>:
> 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.

If random writes are synchronous, it's not relevant anyway, and if they are
asynchronous, a larger dirty buffer pool will boost write performance (allowing
to sort/merge requests before writing). For sequential writes large buffers
don't help a lot.

> 
> 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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