[linux-lvm] label sector and non 512 byte sectors

Stuart D Gathman stuart at bmsi.com
Thu Jan 3 19:13:20 UTC 2013

On Jan 3, Alasdair G Kergon transmitted in part:

> On Wed, Dec 26, 2012 at 09:59:00AM -0500, Phillip Susi wrote:
>> The man page for pvcreate states that the label goes in the second
>> sector.  That means it SHOULD be at an offset of 4096 bytes when using
>> 4096 byte sectors, but apparently it is still at an offset of 512 bytes.
>>  Bug?
> We define a sector at 512 bytes. Always.
> Some documentation could be improved to make that clearer.

And current storage devices always define a logical sector as 512 bytes,
and the firmware takes care of the R/M/W (with caching) needed for
partial or unaligned writes.

The physical sector size is important when *aligning* LVM segments, filesystem
blocks, RAID clusters, etc.

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