[linux-lvm] LVM PV UUID problem

[linux-lvm] LVM PV UUID problem

[Digimer]

Hi all,

  I'm storing LVM information in a postgres database, and wanted to use
the UUID from the PVs / VGs / LVs as the UUIDs in the database. I
noticed when I tried to do this that postgres complained that the UUID
was not valid. I checked with an online UUID validator
(https://www.freecodeformat.com/validate-uuid-guid.php) and it also
reported as invalid.

Example;

====
# pvdisplay | grep UUID
  PV UUID               jLkli2-dEXx-5Y8n-pYlw-nCcy-9dFL-3B6jU3
====

  Is this a known issue?

Thanks for any help/insight!

-- 
Digimer
Papers and Projects: https://alteeve.com/w/
"I am, somehow, less interested in the weight and convolutions of
Einstein’s brain than in the near certainty that people of equal talent
have lived and died in cotton fields and sweatshops." - Stephen Jay Gould

Re: [linux-lvm] LVM PV UUID problem

[Zdenek Kabelac]

Dne 09. 10. 20 v 15:12 Digimer napsal(a):
> Hi all,
> 
>    I'm storing LVM information in a postgres database, and wanted to use
> the UUID from the PVs / VGs / LVs as the UUIDs in the database. I
> noticed when I tried to do this that postgres complained that the UUID
> was not valid. I checked with an online UUID validator
> (https://www.freecodeformat.com/validate-uuid-guid.php) and it also
> reported as invalid.
> 
> Example;
> 
> ====
> # pvdisplay | grep UUID
>    PV UUID               jLkli2-dEXx-5Y8n-pYlw-nCcy-9dFL-3B6jU3
> ====
> 
>    Is this a known issue?
> 

Hi

At the time of lvm2 devel I believe UUID was just a unique identifier,
later some effort to standardize it came in.

But really you should NOT be using basically internal unique identifiers
in your DB - this are internal to DM/LVM work and might be changed at any time 
to something else.

User is supposed to use  'vgname' & 'lvname'  - so there you can put those
valid UUID sequences - although human readable strings are always nicer ;)

Zdenek

Re: [linux-lvm] LVM PV UUID problem

[Digimer]

On 2020-10-09 10:43 a.m., Zdenek Kabelac wrote:
> Dne 09. 10. 20 v 15:12 Digimer napsal(a):
>> Hi all,
>>
>>    I'm storing LVM information in a postgres database, and wanted to use
>> the UUID from the PVs / VGs / LVs as the UUIDs in the database. I
>> noticed when I tried to do this that postgres complained that the UUID
>> was not valid. I checked with an online UUID validator
>> (https://www.freecodeformat.com/validate-uuid-guid.php) and it also
>> reported as invalid.
>>
>> Example;
>>
>> ====
>> # pvdisplay | grep UUID
>>    PV UUID               jLkli2-dEXx-5Y8n-pYlw-nCcy-9dFL-3B6jU3
>> ====
>>
>>    Is this a known issue?
>>
> 
> Hi
> 
> At the time of lvm2 devel I believe UUID was just a unique identifier,
> later some effort to standardize it came in.
> 
> But really you should NOT be using basically internal unique identifiers
> in your DB - this are internal to DM/LVM work and might be changed at
> any time to something else.
> 
> User is supposed to use  'vgname' & 'lvname'  - so there you can put those
> valid UUID sequences - although human readable strings are always nicer ;)
> 
> Zdenek

The trick is that VG and LV names can change, so I wanted to use the
(so-called) UUID as a way to keep track of a given item through name
changes.

I suppose I'll have to rework to use the internal "UUIDs" as more like
serial numbers instead...

-- 
Digimer
Papers and Projects: https://alteeve.com/w/
"I am, somehow, less interested in the weight and convolutions of
Einstein’s brain than in the near certainty that people of equal talent
have lived and died in cotton fields and sweatshops." - Stephen Jay Gould

Re: [linux-lvm] LVM PV UUID problem

[Mark H. Wood]

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On Fri, Oct 09, 2020 at 11:18:38AM -0400, Digimer wrote:
> On 2020-10-09 10:43 a.m., Zdenek Kabelac wrote:
> > Dne 09. 10. 20 v 15:12 Digimer napsal(a):
> >> Hi all,
> >>
> >>    I'm storing LVM information in a postgres database, and wanted to use
> >> the UUID from the PVs / VGs / LVs as the UUIDs in the database. I
> >> noticed when I tried to do this that postgres complained that the UUID
> >> was not valid. I checked with an online UUID validator
> >> (https://www.freecodeformat.com/validate-uuid-guid.php) and it also
> >> reported as invalid.
> >>
> >> Example;
> >>
> >> ====
> >> # pvdisplay | grep UUID
> >>    PV UUID               jLkli2-dEXx-5Y8n-pYlw-nCcy-9dFL-3B6jU3
> >> ====
> >>
> >>    Is this a known issue?
> >>
> > 
> > Hi
> > 
> > At the time of lvm2 devel I believe UUID was just a unique identifier,
> > later some effort to standardize it came in.
> > 
> > But really you should NOT be using basically internal unique identifiers
> > in your DB - this are internal to DM/LVM work and might be changed at
> > any time to something else.
> > 
> > User is supposed to use  'vgname' & 'lvname'  - so there you can put those
> > valid UUID sequences - although human readable strings are always nicer ;)
> > 
> > Zdenek
> 
> The trick is that VG and LV names can change, so I wanted to use the
> (so-called) UUID as a way to keep track of a given item through name
> changes.
> 
> I suppose I'll have to rework to use the internal "UUIDs" as more like
> serial numbers instead...

Well, if we are stuck with non-standard "UUID"s, at least they are
meant to be Universally Unique, so they can be treated as unique
opaque string tokens.  Or you might find a library function that can
return the unencoded binary value and you can encode it as you please.
However, the issue of persistence remains.

FWIW I think it's quite reasonable for someone to want immutable
unique identifiers for distinct objects such as LVM PVs, especially
when the "unique identifier" part is already available and quite
visible.

-- 
Mark H. Wood
Lead Technology Analyst

University Library
Indiana University - Purdue University Indianapolis
755 W. Michigan Street
Indianapolis, IN 46202
317-274-0749
www.ulib.iupui.edu

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Re: [linux-lvm] LVM PV UUID problem

[Marian Csontos]

On 10/9/20 5:39 PM, Mark H. Wood wrote:
> On Fri, Oct 09, 2020 at 11:18:38AM -0400, Digimer wrote:
>> On 2020-10-09 10:43 a.m., Zdenek Kabelac wrote:
>>> Dne 09. 10. 20 v 15:12 Digimer napsal(a):
>>>> Hi all,
>>>>
>>>>  �� I'm storing LVM information in a postgres database, and wanted to use
>>>> the UUID from the PVs / VGs / LVs as the UUIDs in the database. I
>>>> noticed when I tried to do this that postgres complained that the UUID
>>>> was not valid. I checked with an online UUID validator
>>>> (https://www.freecodeformat.com/validate-uuid-guid.php) and it also
>>>> reported as invalid.
>>>>
>>>> Example;
>>>>
>>>> ====
>>>> # pvdisplay | grep UUID
>>>>  �� PV UUID�������������� jLkli2-dEXx-5Y8n-pYlw-nCcy-9dFL-3B6jU3
>>>> ====
>>>>
>>>>  �� Is this a known issue?
>>>>
>>>
>>> Hi
>>>
>>> At the time of lvm2 devel I believe UUID was just a unique identifier,
>>> later some effort to standardize it came in.
>>>
>>> But really you should NOT be using basically internal unique identifiers
>>> in your DB - this are internal to DM/LVM work and might be changed at
>>> any time to something else.
>>>
>>> User is supposed to use� 'vgname' & 'lvname'� - so there you can put those
>>> valid UUID sequences - although human readable strings are always nicer ;)
>>>
>>> Zdenek
>>
>> The trick is that VG and LV names can change, so I wanted to use the
>> (so-called) UUID as a way to keep track of a given item through name
>> changes.
>>
>> I suppose I'll have to rework to use the internal "UUIDs" as more like
>> serial numbers instead...
> 
> Well, if we are stuck with non-standard "UUID"s, at least they are
> meant to be Universally Unique, so they can be treated as unique
> opaque string tokens.  Or you might find a library function that can
> return the unencoded binary value and you can encode it as you please.
> However, the issue of persistence remains.
> 
> FWIW I think it's quite reasonable for someone to want immutable
> unique identifiers for distinct objects such as LVM PVs, especially
> when the "unique identifier" part is already available and quite
> visible.

...and then there is lvconvert which takes existing LV and creates a new 
object with the same name, and original LV is used as a "compnent" (e.g. 
raid1 leg, or snapshot origin)

So now there are two objects, one with the same name, and other one - 
the original LV, which one should use the original UUID?

Just consider LVM UUIDs as MUST BE unique IDs.

Or better MUST BE for lvm to work properly, and SHOULD BE in reality (as 
duplicates occur e.g. when SAN snapshots are visible to the system and 
you run into troubles, and so there are filters,...)

-- Martian

> 
> 
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