[linux-lvm] Filesystem corruption with LVM's pvmove onto a PV with a larger physical block size
ifranzki at linux.ibm.com
Thu Feb 28 08:41:32 UTC 2019
On 28.02.2019 02:31, Cesare Leonardi wrote:
> On 27/02/19 09:49, Ingo Franzki wrote:
>> 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.
>> And yes, its unrelated to encrypted volumes, it can happen with any block device of different physical block sizes that you use as PV.
> Thank you Ingo for the precious informations you are giving here.
> Not to be pedantic, but what do you mean with physical block? Because with modern disks the term is not always clear. Let's take a mechanical disk with 512e sectors, that is with 4k sectors but exposed as 512 byte sectors. Fdisk will refer to it with these terms:
> Sector size (logical/physical): 512 bytes / 4096 bytes
> What you are referring as physical size is actually the logical size reported by fdisk, right? And if it's correct, I guess that should be safe to add the above disk with 512e sectors to an LVM storage composed only by disks with real 512 byte sectors. I expect that from the LVM point of view this should not be even considered a mixed sector size setup, even if the real physical sector size of the added disk is 4096 byte.
> Do you agree or do you think it would be better to test this specific setup?
Well, there are the following 2 commands:
Get physical block size:
blockdev --getpbsz <device>
Get logical block size:
blockdev --getbsz <device>
Filesystems seem to care about the physical block size only, not the logical block size.
So as soon as you have PVs with different physical block sizes (as reported by blockdev --getpbsz) I would be very careful...
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