Il 2020-09-15 20:34 Zdenek Kabelac ha scritto:
Dne 14. 09. 20 v 23:44 Gionatan Danti napsal(a):
Hi all,
I am testing lvmcache with VDO and I have issue with devices block
size.
The big & slow VDO device is on top of a 4-disk MD RAID 10 device
(itself on top of dm-integrity). Over the VDO device I created a
thinpool and a thinvol [1]. When adding the cache device to the volume
group via vgextend, I get an error stating "Devices have inconsistent
logical block sizes (4096 and 512)." [2]
Now, I know why the error shows and what i means. However, I don't
know how to force the cache device to act as a 4k sector device,
and/if this is really required to cache a VDO device.
My current workaround is to set VDO with --emulate512=enabled, but
this can be suboptimal and it is not recommended.
Any idea on what I am doing wrong?
Hi
LVM currently does not support mixing devices of different sector sizes
within
a single VG as it brings lot of troubles we have not yet clear vision
what
to do with all of them.
Hi Zdenek, yes, I understand. What surprised me is that lvmvdo *can* be
combined with caching, and it does not suffer from this issue. Can you
elaborate on why it works in this case?
Also this combination of provisioned devices is not advised - since
you are combining 2 kind of devices on top of each other and it can be
a big problem
to solve recovery case.
True.
On lvm2 side we do not allow to use 'VDO LV' as backend for thin-pool
device.
I noticed it. However, from what I can read on RedHat docs, thinpool
over VDO device should be perfectly fine (the other way around, not so
much).
So ATM it's on a user to solve all the possible scenarios that may
appear on
such device stack.
Zdenek
Thanks.
--
Danti Gionatan
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