On Mon, Mar 7, 2022 at 11:28 AM Yin, Congmin <congmin.yin@xxxxxxxxx> wrote:
>
> If the performance difference between the file system and the raw device is not large in this scenario, then my question is meaningless. But this is not what I can conclude by simply testing two devices. I think your experience will be more reliable. From experience, is there a big performance gap between the two?
I don't think the performance difference would be large, but I could
be wrong -- these things need to be measured, not guessed. Also, it
might be possible to improve the existing file system based approach
by e.g. making sure that the cache file is preallocated, etc.
> According to Jiangpeng's opinion, provide raw devices for each image, such as LVM, on the premise that the performance is greatly improved.
This is certainly an option, but it would significantly worsen the UX
as then the user would need to configure it on a per-image basis. It
should be very easy to modify the code to do this for a single image
case, so I would try to gather some actual performance data first.
Thanks,
Ilya
>
> -----Original Message-----
> From: Ilya Dryomov <idryomov@xxxxxxxxx>
> Sent: Friday, March 4, 2022 6:05 PM
> To: Yin, Congmin <congmin.yin@xxxxxxxxx>
> Cc: dev <dev@xxxxxxx>; Ma, Jianpeng <jianpeng.ma@xxxxxxxxx>
> Subject: Re: consult the performance of creating bdev with file
>
> On Fri, Mar 4, 2022 at 10:04 AM Yin, Congmin <congmin.yin@xxxxxxxxx> wrote:
> >
> > Hi Ilya,
> >
> >
> >
> > Consult a performance question. It is the way of creating bdev that SSD mode of pwl cache is using.
> >
> > Is it appropriate to create bdev devices by truncate files on the file system? Is there a performance gap compared with directly creating bdev device by using /dev /nvme0n1?
>
> I think the file system is used because each RBD image gets should get its own cache. What would handle partitioning the block device between RBD images otherwise?
>
> Thanks,
>
> Ilya
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