* [linux-lvm] lvm-vdo, snapshots and cache
@ 2022-11-15 17:42 Gionatan Danti
2022-11-15 21:56 ` Zdenek Kabelac
0 siblings, 1 reply; 6+ messages in thread
From: Gionatan Danti @ 2022-11-15 17:42 UTC (permalink / raw)
To: LVM general discussion and development
Dear all,
as previous vdo utils are gone in RHEL9, VDO volumes must be created via
lvm-vdo and associated lvm commands.
What is not clear to me is how to combine lvm-vdo with lvmthin (for fast
CoW snapshots) and/or lvmcache (for SSD caching of an HDD pool). For
example, with the old /dev/mapper/vdo style volumes (ie: the one created
via vdo create) one can do something as physical_dev -> vdo -> lvmthin
-> lvmcache.
How to do the same with lvm-vdo?
Regards.
--
Danti Gionatan
Supporto Tecnico
Assyoma S.r.l. - www.assyoma.it
email: g.danti@assyoma.it - info@assyoma.it
GPG public key ID: FF5F32A8
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^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [linux-lvm] lvm-vdo, snapshots and cache
2022-11-15 17:42 [linux-lvm] lvm-vdo, snapshots and cache Gionatan Danti
@ 2022-11-15 21:56 ` Zdenek Kabelac
2022-11-15 22:41 ` Gionatan Danti
0 siblings, 1 reply; 6+ messages in thread
From: Zdenek Kabelac @ 2022-11-15 21:56 UTC (permalink / raw)
To: LVM general discussion and development, Gionatan Danti
Dne 15. 11. 22 v 18:42 Gionatan Danti napsal(a):
> Dear all,
> as previous vdo utils are gone in RHEL9, VDO volumes must be created via
> lvm-vdo and associated lvm commands.
>
> What is not clear to me is how to combine lvm-vdo with lvmthin (for fast CoW
> snapshots) and/or lvmcache (for SSD caching of an HDD pool). For example, with
> the old /dev/mapper/vdo style volumes (ie: the one created via vdo create) one
> can do something as physical_dev -> vdo -> lvmthin -> lvmcache.
>
> How to do the same with lvm-vdo?
Hi
You could try 'vg' on top of another 'vg' - however I'd not recommend to use
it this way (and it's unssuported (&unsupportable) by lvm2 in general)
We aim to support multiple VDO LV within a single VDOPOOL - will hopefully
happen relatively soon (so it should work like with thin pools)
IMHO I'd not recommend to combine 2 provisioning technologies - it's already
hard to resolve 'out-of-space' troubles with just one technology...
We will see if the 'VDO thick snapshot' will also go with multiple VDO LV
support - likely not - but will be added later on.
Caching should be already support - on VDO LV as well as on VDOPOOL LV (both
work somewhat differently).
Regards
Zdenek
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^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [linux-lvm] lvm-vdo, snapshots and cache
2022-11-15 21:56 ` Zdenek Kabelac
@ 2022-11-15 22:41 ` Gionatan Danti
2022-11-16 10:50 ` Zdenek Kabelac
0 siblings, 1 reply; 6+ messages in thread
From: Gionatan Danti @ 2022-11-15 22:41 UTC (permalink / raw)
To: Zdenek Kabelac; +Cc: LVM general discussion and development
Il 2022-11-15 22:56 Zdenek Kabelac ha scritto:
> You could try 'vg' on top of another 'vg' - however I'd not recommend
> to use it this way (and it's unssuported (&unsupportable) by lvm2 in
> general)
Hi Zdenek,
yeah, I would strongly avoid that outside lab testing.
> IMHO I'd not recommend to combine 2 provisioning technologies - it's
> already hard to resolve 'out-of-space' troubles with just one
> technology...
The issue is that fast snapshots are only provided by dm-thin, meaning
that lvmthin is almost mandatory for implementing a rolling/continuous
snapshot scheme. And, on a more basic level, if we can not stack LVM on
top of a VDO LV (in a supported manner), how can we take a snapshot of
user data residing on that specific volume?
This seems a clear regression vs a separate VDO device. Am I missing
something?
> Caching should be already support - on VDO LV as well as on VDOPOOL LV
> (both work somewhat differently).
Good, thanks for confirming. I will do some tests...
Regards.
--
Danti Gionatan
Supporto Tecnico
Assyoma S.r.l. - www.assyoma.it
email: g.danti@assyoma.it - info@assyoma.it
GPG public key ID: FF5F32A8
_______________________________________________
linux-lvm mailing list
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https://listman.redhat.com/mailman/listinfo/linux-lvm
read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [linux-lvm] lvm-vdo, snapshots and cache
2022-11-15 22:41 ` Gionatan Danti
@ 2022-11-16 10:50 ` Zdenek Kabelac
2022-11-16 14:38 ` Gionatan Danti
0 siblings, 1 reply; 6+ messages in thread
From: Zdenek Kabelac @ 2022-11-16 10:50 UTC (permalink / raw)
To: Gionatan Danti; +Cc: LVM general discussion and development
Dne 15. 11. 22 v 23:41 Gionatan Danti napsal(a):
> Il 2022-11-15 22:56 Zdenek Kabelac ha scritto:
>> You could try 'vg' on top of another 'vg' - however I'd not recommend
>> to use it this way (and it's unssuported (&unsupportable) by lvm2 in
>> general)
>
> Hi Zdenek,
> yeah, I would strongly avoid that outside lab testing.
>
>> IMHO I'd not recommend to combine 2 provisioning technologies - it's
>> already hard to resolve 'out-of-space' troubles with just one
>> technology...
>
> The issue is that fast snapshots are only provided by dm-thin, meaning that
> lvmthin is almost mandatory for implementing a rolling/continuous snapshot
> scheme. And, on a more basic level, if we can not stack LVM on top of a VDO LV
> (in a supported manner), how can we take a snapshot of user data residing on
> that specific volume?
Well - as said - vg on vg is basically equivalent of the original LV on top of
VDO manager.
But still these fast snapshot do not solve you a problem of double
out-of-space fault.
> This seems a clear regression vs a separate VDO device. Am I missing something?
It's good for experimenting - but I'd not suggest to use this setup.
Regards
Zdenek
_______________________________________________
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^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [linux-lvm] lvm-vdo, snapshots and cache
2022-11-16 10:50 ` Zdenek Kabelac
@ 2022-11-16 14:38 ` Gionatan Danti
2022-11-16 15:35 ` Zdenek Kabelac
0 siblings, 1 reply; 6+ messages in thread
From: Gionatan Danti @ 2022-11-16 14:38 UTC (permalink / raw)
To: Zdenek Kabelac; +Cc: LVM general discussion and development
Il 2022-11-16 11:50 Zdenek Kabelac ha scritto:
> Well - as said - vg on vg is basically equivalent of the original LV
> on top of VDO manager.
Hi Zdenek,
it seems clunkier to manage two nested VG/LV if you ask me.
> But still these fast snapshot do not solve you a problem of double
> out-of-space fault.
Yeah, but available space requires constant monitor even when dealing
with lvmthin.
> It's good for experimenting - but I'd not suggest to use this setup.
In RHEL7 it was specifically supported - see here[1]:
"As a general rule, you should place certain storage layers under VDO
and others on top of VDO:
Under VDO: DM-Multipath, DM-Crypt, and software RAID (LVM or mdraid).
On top of VDO: LVM cache, LVM snapshots, and LVM Thin Provisioning"
For a practical example: in the past I experimented with a storage stack
composed of raid -> vdo -> lvmthin -> xfs serving qemu/kvm virtual disk
files. The lvmthin layer enabled rolling snapshots, and was a key
feature of the test setup.
Now the only method to replicate that is to have two nested LVM
instances, one running vdo and one lvmthin - right?
Regards.
[1]
https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/storage_administration_guide/vdo-qs-requirements
--
Danti Gionatan
Supporto Tecnico
Assyoma S.r.l. - www.assyoma.it
email: g.danti@assyoma.it - info@assyoma.it
GPG public key ID: FF5F32A8
_______________________________________________
linux-lvm mailing list
linux-lvm@redhat.com
https://listman.redhat.com/mailman/listinfo/linux-lvm
read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [linux-lvm] lvm-vdo, snapshots and cache
2022-11-16 14:38 ` Gionatan Danti
@ 2022-11-16 15:35 ` Zdenek Kabelac
0 siblings, 0 replies; 6+ messages in thread
From: Zdenek Kabelac @ 2022-11-16 15:35 UTC (permalink / raw)
To: Gionatan Danti; +Cc: LVM general discussion and development
Dne 16. 11. 22 v 15:38 Gionatan Danti napsal(a):
> Il 2022-11-16 11:50 Zdenek Kabelac ha scritto:
>> Well - as said - vg on vg is basically equivalent of the original LV
>> on top of VDO manager.
>
> Hi Zdenek,
> it seems clunkier to manage two nested VG/LV if you ask me.
IMHO not different from lvm on top of vdo managed volume.
It should be mostly equal (and in few cases possibly even easier or at least
more OS friendly)
>
>> But still these fast snapshot do not solve you a problem of double
>> out-of-space fault.
>
> Yeah, but available space requires constant monitor even when dealing with
> lvmthin.
>
>> It's good for experimenting - but I'd not suggest to use this setup.
>
> In RHEL7 it was specifically supported - see here[1]:
>
> "As a general rule, you should place certain storage layers under VDO and
> others on top of VDO:
> Under VDO: DM-Multipath, DM-Crypt, and software RAID (LVM or mdraid).
> On top of VDO: LVM cache, LVM snapshots, and LVM Thin Provisioning"
>
> For a practical example: in the past I experimented with a storage stack
> composed of raid -> vdo -> lvmthin -> xfs serving qemu/kvm virtual disk files.
> The lvmthin layer enabled rolling snapshots, and was a key feature of the test
> setup.
>
> Now the only method to replicate that is to have two nested LVM instances, one
> running vdo and one lvmthin - right?
>
Well - it's not difficult 'coding' to enable using 'VDO LV' as thinpool data
LV, however we currently lack a lot on support for 'VDO LV' recovery alone in
lvm2 - so until this will get polished - we try to avoid shot ourself to our
foots with enabling these complicated stacks ATM :)
We also have some ideas for different snapshoting inside VDO - so we will see
how that will go - it looks more supportable then combining VDO+THIN together.
Regards
Zdenek
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2022-11-15 17:42 [linux-lvm] lvm-vdo, snapshots and cache Gionatan Danti
2022-11-15 21:56 ` Zdenek Kabelac
2022-11-15 22:41 ` Gionatan Danti
2022-11-16 10:50 ` Zdenek Kabelac
2022-11-16 14:38 ` Gionatan Danti
2022-11-16 15:35 ` Zdenek Kabelac
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