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Thu, 29 Sep 2022 05:12:09 -0700 (PDT) In-Reply-To: <7f7db1ac-fe8a-851f-ef38-8aa85f9353c2@gmail.com> References: <6c03a8e8-c4ed-4c2a-a23b-bf4513577d1e@gmail.com> <6f7d32a9-a6f3-44b7-a4be-53c9372e00b4@gmail.com> <7f7db1ac-fe8a-851f-ef38-8aa85f9353c2@gmail.com> X-Referenced-Uid: 71096 Thread-Topic: Re: LVM2 Metadata structure, extents ordering, metadata corruptions User-Agent: Android X-Is-Generated-Message-Id: true MIME-Version: 1.0 X-Local-Message-Id: <06aa39c6-66bc-45be-8a69-07fd827db5bf@gmail.com> From: Roberto Fastec Date: Thu, 29 Sep 2022 14:12:06 +0200 To: Zdenek Kabelac Message-ID: <06aa39c6-66bc-45be-8a69-07fd827db5bf@gmail.com> X-Mimecast-Impersonation-Protect: Policy=CLT - Impersonation Protection Definition; Similar Internal Domain=false; Similar Monitored External Domain=false; Custom External Domain=false; Mimecast External Domain=false; Newly Observed Domain=false; Internal User Name=false; Custom Display Name List=false; Reply-to Address Mismatch=false; Targeted Threat Dictionary=false; Mimecast Threat Dictionary=false; Custom Threat Dictionary=false X-Scanned-By: MIMEDefang 3.1 on 10.11.54.5 X-Mailman-Approved-At: Fri, 30 Sep 2022 07:11:51 +0000 Subject: Re: [linux-lvm] LVM2 Metadata structure, extents ordering, metadata corruptions X-BeenThere: linux-lvm@redhat.com X-Mailman-Version: 2.1.29 Precedence: list List-Id: LVM general discussion and development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: LVM general discussion and development Cc: LVM general discussion and development Errors-To: linux-lvm-bounces@redhat.com Sender: "linux-lvm" X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/mixed; boundary="===============6685080291748292605==" --===============6685080291748292605== Content-Type: multipart/alternative; boundary="----RWMS6QTY2V55LSDWV4Q04AVMKA5GKC" ------RWMS6QTY2V55LSDWV4Q04AVMKA5GKC Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Thank you for all the details and for your kind replies I will have a look to the utilities you kindly pointed out Kind regards=20 Il giorno 29 set 2022, 13:41, alle ore 13:41, Zdenek Kabelac ha scritto: >Dne 29. 09. 22 v 13:15 Roberto Fastec napsal(a): >> Hello Zdenek >> Thank you for the explanation >>=20 >> May I kindly ask you what/which is the command line API to access and > >> manipulate those metadata? >>=20 > >'command line API' in the mean of: > >To create LV -- 'lvcreate'.... >To remove LV -- 'lvremove'.... > > >Note - many command can actually work without physical interaction with >DM=20 >layer (--driverloaded n) - however in some case some targets require >presence=20 >of DM. > >lvm2 commands are the way how to change your metadata properly. > > >> And when you say vi editor, do you kindly mean direct edit of HEX >values on=20 >> the raw metadata? > >No way - you can't change metadata on disk - unless you would be >basically=20 >precisely copying what lvm2 command does - so what would be the point >?? > >Simply use lvm2 command to make the job. Unless I'm missing some >important=20 >point why would you need to work with lvm2 metadata but without lvm2 >?? > > >>=20 >> Thank you >>=20 >> If you kindly may have some link to some documentation, thank you >even more >>=20 >> Though here it is not the configuration that got lost > >Well yeah - it will take some time - but i.e. RHEL storage >documentation might=20 >be a good way to go through it. > > > >> Also, additional info, we now got that all the cases do have active >the=20 >> thin-provisionin and looks like that these are additional/different >metadata=20 >> tables > >This-provisioning is handled by LVM2 only to provide LVs for metadata >and=20 >data LVs - and then the thinLVs to a user. > >Physical block layout for thin-provisioning is fully stored inside=20 >thin-pool's metadata device. > >To explore those mappings you need to use tools like 'thin_dump', >'thin_ls' > >>=20 >> So if these got messed/corrupted... >>=20 > >If these thin-pool metadata get corrupted, there is tool: >'thin_repair'. > >Note: corruption of some high-level bTree nodes may result a severe >damage to=20 >whole metadata structure -> i.e. lots of thinLVs being lost. > >It's a good idea to keep such metadata on some resilient type of >storage=20 >(raid) and of course rule #1 - create regular backups of your thin=20 >volumes... (snapshot of thinLV is not a backup!). > > >> In QNAP looks they have made some customization and so thin-provision >LVM=20 >> metadata are on a dedicated partition >>=20 >> we observed the HEX inside there and got partially the logic >>=20 >> About thin-provisioning, again, any "fsck"-like is available? (I >suppose no,=20 >> but just as confirmation) > >This tool is called 'thin_check' > >(and this tool is in fact executed with every thin-pool activation &=20 >deactivation by default by lvm2) > >Note: just like with lvm2 metadata - also thin-pool's kernel metadata >are=20 >check-summed (protected agains disc bit corruptions), so again zero >chance=20 >with any 'hex-editor' to manipulate them - unless you would 'recreate'=20 >thin-pool engine... > > >Regards > >Zdenek ------RWMS6QTY2V55LSDWV4Q04AVMKA5GKC Content-Type: text/html; charset=utf-8 Content-Transfer-Encoding: quoted-printable
Thank you fo= r all the details and for your kind replies

I will have a look to the utilities you kindly pointed ou= t

Kind regards
Il giorno 29 set 2022, alle ore 13:41, Zdenek K= abelac <zd= enek.kabelac@gmail.com> ha scritto:
Dne 29. 09. 22 v 13:15 Roberto Fastec napsal(a):
 Hello Zdenek
 Thank you for=
 the explanation
 
 May I kindly ask you what/which is the command li=
ne API to access and 
 manipulate those metadata?
<= br>'command line API' in the mean of:

To create LV -- 'lvcreate'..= ..
To remove LV -- 'lvremove'....


Note - many command can a= ctually work without physical interaction with DM
layer (--driverloade= d n) - however in some case some targets require presence
of DM.
lvm2 commands are the way how to change your metadata properly.

And when you say vi editor= , do you kindly mean direct edit of HEX values on
the raw metadata?

No way - you can't change metadata on disk - unless you = would be basically
precisely copying what lvm2 command does - so what= would be the point ??

Simply use lvm2 command to make the job. Unl= ess I'm missing some important
point why would you need to work with l= vm2 metadata but without lvm2 ??



Thank you

If you kindly may have some link t= o some documentation, thank you even more

Though here it is not th= e configuration that got lost

Well yeah - it will take = some time - but i.e. RHEL storage documentation might
be a good way to = go through it.




So if these got messed/corrupted...

If these thin-pool metadata get corrupted, there is = tool: 'thin_repair'.

Note: corruption of some high-level bTree nodes= may result a severe damage to
whole metadata structure -> i.e. lot= s of thinLVs being lost.

It's a good idea to keep such metadata on s= ome resilient type of storage
(raid) and of course rule #1 - create r= egular backups of your thin
volumes... (snapshot of thinLV is not a b= ackup!).


In QNAP= looks they have made some customization and so thin-provision LVM
met= adata are on a dedicated partition

we observed the HEX inside ther= e and got partially the logic

About thin-provisioning, again, any = "fsck"-like is available? (I suppose no,
but just as confirmation)
=

This tool is called 'thin_check'

(and this tool is= in fact executed with every thin-pool activation &
deactivation by= default by lvm2)

Note: just like with lvm2 metadata - also thin-poo= l's kernel metadata are
check-summed (protected agains disc bit corrupt= ions), so again zero chance
with any 'hex-editor' to manipulate them - = unless you would 'recreate'
thin-pool engine...


Regards
<= br>Zdenek


------RWMS6QTY2V55LSDWV4Q04AVMKA5GKC-- --===============6685080291748292605== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline _______________________________________________ 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/ --===============6685080291748292605==--