LVM SSD Cachepool how enable fstrim

[marco__mg]

Hello to everybody, I was playing with LVM and I was setting up a volume with ext4 on an HDD and I want to use an SSD as a cache.

What I first done was

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lvcreate --type cache-pool -l 100%FREE -n datacache SSD /dev/sda3
lvcreate --type cache -l 100%FREE -n data --cachepool datacache SSD --cachemode writeback /dev/sdb1

So respectivily I created a cache-pool voume called datacache and than a vomume called data attached to datacache.

I think (the problem is I don't remember) that fstrim works perfectly in this way.

Then I had to do some operations on disk and I had to deattach my cache. So I uncached my disk

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lvconvert --uncache /dev/mapper/SSD-data

Then I moved the disk (and other thinks) and at the end I reattached my disk to a cache-pool

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lvcreate --type cache-pool -l 100%FREE -n datacache SSD /dev/sda3
lvconvert --type cache --cachemode writeback --cachepool datacache SSD/data

The problem is that now if I fstrim i obtain

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root@me:~# fstrim -a
fstrim: /mnt/data: FITRIM ioctl failed: Argument not valid

I am not completly sure that before detaching and reattaching the cache it worked, but I suppose to because I tested fstrim and I don't remember any errors.

I am using debian buster.

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root@me:~# uname -a
Linux me 4.19.0-14-amd64 #1 SMP Debian 4.19.171-2 (2021-01-30) x86_64 GNU/Linux

Thank you in advice. If I missed some important information I am really sorry. Tell me what you need and I'll post it