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lvm utilities, metadata format, CRC (checksum)

linux-lvm Michael Jensen 3 participants 5 messages Dec 6, 2008 – Dec 9, 2008

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Michael Jensen

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Attempts to use the lvm cli tools have not proven sucessful to date.

Here's the scenario -

- A master volume is presented to the host and is init'd for use with LVM and mounted (and cannot be dismounted).
- Sometime later a storage manged snapshot is created and then mapped (presented) to the same host.  This LUN has identical data in the metadata area (1st 256 sectors).  The only blocks that are different would be where writes have been made to the master since the snapshot was taken.
- a pvscan made after the snap is available to the host reports duplicate uuid,  And it appears that it shifts the systems view of which LUN is the one representing the LVM volume if the snap LUN is a higher numbered LUN than the master.
- filtering the master out via the conf file and doing a scan (which purges cache, etc) has not helped as the master LUN is already known to LVM and is mounted.

A couple of questions -

- what is the best tool to use to search all the archive files?
- what sequence are you suggesting with the tools that will avoid the duplicate found??

thanks
mike

--- On Fri, 12/5/08, Alasdair G Kergon <[email protected]> wrote:

Quoted 1 line · Michael Jensen

Earlier attempts at being able to get a storage based snapshot on the same

server as its master failed because -

Quoted 3 lines

- the master is always mounted (production)
- the utilities recognize both master and snap and declare duplicate
- manual edits of the header and label field failed because both are

"wrapped" with CRC that is calculated and checked by the utilities

That was obfuscated deliberately to dissuade people from thinking it's OK to
edit those fields directly on disk instead of using the supplied tools!

Search the list archives - the topic comes up regularly and you can do what you need using the command line tools.

Alasdair

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#1 lore raw
Quoted 1 line · Michael Jensen

- what is the best tool to use to search all the archive files?

Google.

Quoted 1 line

- what sequence are you suggesting with the tools that will avoid the duplicate found??

�
You're doing nothing new here - read the archives.

Alasdair

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#2 lore raw
Quoted 8 lines · Alasdair G Kergon
Quoted 1 line · Michael Jensen

- what is the best tool to use to search all the archive files?

Google.

Quoted 1 line

- what sequence are you suggesting with the tools that will avoid the duplicate found??

You're doing nothing new here - read the archives.

D�j� vu...

http://www.redhat.com/archives/linux-lvm/2007-November/msg00039.html

Perhaps this info should be added to the wiki. I just tried to add something to the FAQ section, but it looks like the page is immutable (or I'm just not looking hard enough).

http://sources.redhat.com/lvm2/wiki/FrequentlyAskedQuestions

--Dave

#3 lore raw
Quoted 7 lines · David Robinson
Quoted 1 line · Alasdair G Kergon

On Fri, Dec 05, 2008 at 04:07:30PM -0800, Michael Jensen wrote:

Perhaps this info should be added to the wiki. I just tried to add something to the FAQ section, but it looks like the page is immutable (or I'm just not looking hard enough).

http://sources.redhat.com/lvm2/wiki/FrequentlyAskedQuestions

Unfortunately the wiki has suffered from spam problems. I tried to give you access to edit, but yet again the buggy software has locked out my own account.

Alasdair

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#4 lore raw
In reply to Alasdair G Kergon


Below is a "cleaned up" version of the posting from Nov 2007 to clone a volume group. Did I correctly interpret the instructions/text??


From: Alasdair G Kergon <agk redhat com>
To: LVM general discussion and development <linux-lvm redhat com>
Subject: Re: [linux-lvm] Steps to "clone" a volume group
Date: Thu, 22 Nov 2007 16:05:40 +0000
--------------------------------------------------------------------------------

Quoted 9 lines

1. For each original PV, create a filter entry in /etc/lvm/lvm.conf to temporarily mask the PV from the LVM tools.

2. Create a temporary alternative lvm system directory holding a copy of lvm.conf that has filters to accept only
the new copies of the PVs and set LVM_SYSTEM_DIR to use it.
3. Create the cloned PV(s)
4. Modify the cloned volume group name, ID and physical volume IDs to avoid name and UUID clashes between the original and cloned devices:

(with LVM_SYSTEM_DIR set)

Quoted 2 lines

5. Remove filtering rules & verify both VGs co-exist correctly
6. discard LVM_SYSTEM_DIR env var & directory

--- On Fri, 12/5/08, Alasdair G Kergon <[email protected]> wrote:

From: Alasdair G Kergon <[email protected]>
Subject: Re: [linux-lvm] lvm utilities, metadata format, CRC (checksum)
To: "Michael Jensen" <[email protected]>
Cc: [email protected]
Date: Friday, December 5, 2008, 6:01 PM

Quoted 1 line · Michael Jensen

- what is the best tool to use to search all the archive files?

Google.

Quoted 1 line

- what sequence are you suggesting with the tools that will avoid the

duplicate found??

You're doing nothing new here - read the archives.

Alasdair

Signature · 7 lines
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