How does LVM provide erased storage?

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1

Hi,

I wonder how LVM makes sure to not expose data written in a previous qube when providing storage to another qube.

Any idea where I could find some documentation about this?

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2

IIUC this is controlled by the /etc/lvm/lvm.conf option thin_pool_zero, enabled by default. See the “Zeroing” section in lvmthin(7).

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3

this is exactly what I was looking for, thanks!

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4

Any idea how this mechanism is applied for a BTRFS backend?

5

For Btrfs and anything else backed by file-reflink (or even the legacy ‘file’ driver), a new volume is created as a sparse file, using the ftruncate syscall to extend a new zero length file to the volume size. Afterwards, “the extended part reads as null bytes”.

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