Re: [linux-lvm] Why is the performance of my lvmthin snapshot so poor

From: Demi Marie Obenour <demi@invisiblethingslab.com>
To: LVM general discussion and development <linux-lvm@redhat.com>,
	Zhiyong Ye <yezhiyong@bytedance.com>
Subject: Re: [linux-lvm] Why is the performance of my lvmthin snapshot so poor
Date: Wed, 15 Jun 2022 12:39:03 -0400	[thread overview]
Message-ID: <YqoLTvinIjf9BetH@itl-email> (raw)
In-Reply-To: <fd171a18d82d6f496d9d75c966278b88@assyoma.it>

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On Wed, Jun 15, 2022 at 02:40:29PM +0200, Gionatan Danti wrote:
> Il 2022-06-15 11:46 Zhiyong Ye ha scritto:
> > I also think it meets expectations. But is there any other way to
> > optimize snapshot performance at the code level? Does it help to
> > reduce the chunksize size in the code, I see in the help documentation
> > that the chunksize can only be 64k minimum.
> 
> I don't think forcing the code to use smaller recordsize is a good idea.
> Considering the hard limit on metadata size (16 GB max), 64K chunks are good
> for ~16 TB thin pool - already relatively small.
> 
> A, say, 16K recordsize would be good for a 4 TB pool only, an so on.
> Moreover, sequential performance will significantly suffer.
> 
> I think you have to accept the performance hit on first chunck allocation &
> rewrite.

I seriously hope this will be fixed in dm-thin v2.  It’s a significant
problem for Qubes OS.

-- 
Sincerely,
Demi Marie Obenour (she/her/hers)
Invisible Things Lab

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