On Jul 28, 2018, at 1:28 PM, Henrique de Moraes Holschuh <h...@debian.org>
wrote:
> On Sat, 28 Jul 2018, David Wright wrote:
>> On Sat 28 Jul 2018 at 10:57:45 (-0300), Henrique de Moraes Holschuh wrote:
>>> On Sat, 28 Jul 2018, Rick Thomas wrote:
>>>>> rbthomas@small:~$ lsblk -t
>>>>> NAME ALIGNMENT MIN-IO OPT-IO PHY-SEC LOG-SEC ROTA SCHED
>>>>> RQ-SIZE RA WSAME
>>>>> sda 0 4096 33553920 4096 512 1 mq-deadline
>>>>> 60 128 0B
>>>>> `-sda1 0 4096 33553920 4096 512 1 mq-deadline
>>>>> 60 128 0B
>>>>> |-small-swap -1 4096 0 4096 512 1
>>>>> 128 128 32M
>>>>> |-small-root -1 4096 0 4096 512 1
>>>>> 128 128 32M
>>>>> `-small-home -1 4096 0 4096 512 1
>>>>> 128 128 32M
>>>>> mmcblk2 0 512 0 512 512 0 mq-deadline
>>>>> 128 128 0B
>>>>> |-mmcblk2p1 0 512 0 512 512 0 mq-deadline
>>>>> 128 128 0B
>>>>> `-mmcblk2p2 0 512 0 512 512 0 mq-deadline
>>>>> 128 128 0B
>>>>> rbthomas@small:~$
>>>>
>>>> Note the alignment values of “-1” for the lvm entries but not for the GPT
>>>> partition or the whole disk.
>>>> Why do you suppose that is?
>>>
>>> Keep in mind that you *offset*-align the outer container *only*, and then
>>> inside
>>> you just keep the size alignment.
>>>
>>> So, the above ensures correct use of the partitions even if sda1 is
>>> unaligned.
>>>
>>> If you offset-align sda1 to -1, everything inside it should have an offset
>>> of
>>> zero to keep the alignment correct.
>>
>> I don't think I fully understand the explanation. Can you point out
>> the number(s) that's wrong, and how it should be corrected.
>
> There is nothing wrong on the table above as far as I can tell,
> *assuming* the device does need the -1 alignment. Since sda1 isn't
> aligned, everything inside it at the first level must be (and is)
> aligned at -1 to compensate.
>
> Where sda1 aligned at -1, nothing inside it should be, as sda1 would
> already provide the required alignemnt to anything inside it.
Thanks for the clarification, Henrique!
Let me see if I have this right…
1) If I had heeded the warning in “man pvcreate” and set up the physical volume
with
pvcreate —dataalignmentoffset 7s /dev/sda
to accommodate the -1 offset (provided either by the drive itself or the USB
enclosure it is in — we don’t know) then all the “-1”s in the above table would
be “0”s and I would not be getting the error messages at boot time. Is this
correct?
2) But as it is, I did not do that, so when I used vgcreate to make the volume
group called “small”, it realized that the partition was out of alignment and
compensated — thus causing the alignment of “-1” for all of the logical
volumes. And, most importantly, therefor the logical volumes are, in fact,
properly aligned and I can stop worrying. Furthermore, the warnings at boot
time are just noting that an alignment of “-1” has been applied by the
device-mapper and all is well. Is this correct?
3) Or are you saying that the messages are _not_ just warnings: I should go
back and re-format the disk to use the “—dataalignmentoffset 7s” option. (I
can do this if I do it soon. I don’t have much data on the disk yet.)
Thanks,
Rick
