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From: Zdenek Kabelac <zkabelac@redhat.com>
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Date: Mon, 21 Jan 2019 21:19:52 +0100
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Subject: Re: [linux-lvm] Unable to un-cache logical volume when chunk size
	is over 1MiB
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To: LVM general discussion and development <linux-lvm@redhat.com>, Douglas Paul <doug@bogon.ca>

Dne 18. 07. 18 v 16:58 Douglas Paul napsal(a):
> On Wed, Jul 18, 2018 at 03:25:10PM +0100, Ryan Launchbury wrote:
>> Does anyone have any other ideas or potential workarounds for this issue?
>>
>> Please let me know if you require more info.
> 
> I didn't see this in the previous messages, but have you tried temporarily
> remounting the filesystems read-only if you can't unmount them?
> 
> Also, earlier you mentioned looking at /var/log/dmesg for write errors.  On
> my systems, that only contains a snapshot at boot. I have to run dmesg to
> see the latest updates. It seems suspicious to have nothing in the dmesg
> during 61 days past 10 seconds after system boot ...
> 

Hi

So this should help:

lvchange --cachesettings  migration_threshold=16384 vg/cacheLV

the problem was the usage of unexpectedly big chunk sizes,
that are used when cache-pool size is big (>TiB) and chunksizes
are  >= 1MiB.

Upstream has committed patches for automatic protection against too small
migration threshold.


Zdenek