[linux-lvm] Filesystem corruption with LVM's pvmove onto a PV with a larger physical block size

Ingo Franzki ifranzki at linux.ibm.com
Wed Feb 27 08:49:35 UTC 2019

On 27.02.2019 01:00, Cesare Leonardi wrote:
> On 25/02/19 16:33, Ingo Franzki wrote:
>> we just encountered an error when using LVM's pvmove command to move the data from an un-encrypted LVM physical volume onto an encrypted volume.
>> After the pvmove has completed, the file system on the logical volume that resides on the moved physical volumes is corrupted and all data on this LV is lost.
> Hello, your message is interesting. And also this thread:
> https://www.redhat.com/archives/linux-lvm/2019-February/msg00002.html
> But I'd like to know if I understood correctly.
> Should I care about the physical disk size when I use LVM? Mixing disk with different sector size (512b and 4k) is dangerous?

As far as I can tell: Yes if you pvmove data around or lvextend an LV onto another PV with a larger physical block size that is dangerous.
Creating new LVs and thus new file systems on mixed configurations seem to be OK. 

> Your message and others from the other thread, seems to say that LVM doesn't handle correctly that situation and that if I pvmove data between a 512b disk and a 4k disk (or viceversa), it will lead to a massive filesystem corruption. If I understood correctly, the problem that you described looks unrelated to encrypted volume and was only exacerbated by that. Right?

Moving from 512 to 4096 seems to cause FS corruption, moving from 4096 to 512 does not. So I guess its only a problem when moving to larger physical block sizes.

And yes, its unrelated to encrypted volumes, it can happen with any block device of different physical block sizes that you use as PV.
E.g. SCSI disks exist in 512 bytes block size and 4096 bytes block size. Or s390-DASDs which always have 4096 bytes blocks. 

We just encountered it using encrypted disks with the sector-size option to increase encryption performance. 
So actually we want people to use larger sector sizes, but this seems to cause problems with LVM. 

The good thing about the example with encrypted volumes on loopback devices is that you can reproduce the problem on any platform, without having certain hardware requirements.

> Cesare.

Ingo Franzki
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