On Thu, 28 Feb 2019, Cesare Leonardi wrote:
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?
I would definitely test it, using the same test script that reproduces the
problem with loopback devices.
That said, I believe you are right - it should definitely work. Most of
my drives are 512/4096 logical/phys. If you actually write a single 512
byte sector, however, the disk firmware will have to do a
read/modify/write cycle - which can tank performance.
hdparm will report logical and physical sector size - but there doesn't
seem to be an option to set logical sectory size. There really is no
need once you already support a smaller logical sector size, as the
performance hit can be avoided by aligned filesystems with 4k+ block
size (most modern filesystems).
Once I encountered a bug in drive firmware where the R/M/W did not
work correctly with certain read/write patterns (involving unaligned
multi sector writes). I do not wish that on anyone. (don't worry,
that drive model is long gone...).
--
Stuart D. Gathman <stuart@xxxxxxxxxxx>
"Confutatis maledictis, flamis acribus addictis" - background song for
a Microsoft sponsored "Where do you want to go from here?" commercial.
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