Re: Beating a dead horse

[Robert Elz <kre%munnari.OZ.AU@localhost>]

    Date:        Thu, 26 Nov 2015 09:11:22 +0000 (UTC)
    From:        mlelstv%serpens.de@localhost (Michael van Elst)
    Message-ID:  <n36ibq$acf$3%serpens.de@localhost>

  | LVM scans for devices and has a filter regex configured in
  | /etc/lvm/lvm.conf.

OK, I think that wasn't the problem ... I tried everything I could think
of as the filter list in there, with and without /dev/ (and with and
without /dev/ as the arg to lvcreate and nothing made a difference).

Then I had an epiphany, and tried rdk13 instead, that one worked...
(linux, and its doc, are all evil.)

That's enough for me to conclude that lvm doesn't work (properly) with
4k sector size disks either - that is, I made a vg, on the pv, and looked
at its size and it (just like cgd) is 1/8 of the size that it should be.
That is, it tells me 120GB approx on dk13 which is a 1TB approx slice of
the 3TB drive (at the minute, since it is not working usefully, I'm just
playing around on it.)

So, I presume (without going to look at its code, which being from linux
it seems, I expect would make me ill ... but that's just from normal
experience, I have no idea if lvm is as bad as most other linux code or not)
that it suffers in just the same way as cgd, gets the count of sectors, and
simply presumes they are 512 bytes each, and then makes things that big.

Again, that "works" in the sense that everything should function correctly
(provided we keep all block sizes as multiples of 4096) but means that my
3TB drive with 4K sectors has less usable space than if I had bought a much
cheaper 512GB drive with 512 byte sectors...

Once again, and just for completeness, if I just put a FFS on it, that works
properly, and all the space is available, but I don't want an unencrypted
ffs to store backups on a removable drive...

Sometime early next year (if no-one else has done it before then) I'll
work out a rational fix for this, and make it work, until then this drive
can just sit on the shelf, and I'll continue with backups to my (getting
close to full) smaller (512 byte sector) (encrypted) removable drives...

kre