topic Re: does the mirroring supported by LVM ( LINUX ) in Operating System - Linux

does the mirroring supported by LVM ( LINUX )

skt_skt — Tue, 26 Jun 2007 22:24:20 GMT

idont see an option for mirroring on the man page for lvextend. is the mirroring not supported on Linux/LVM

Re: does the mirroring supported by LVM ( LINUX )

Stuart Browne — Tue, 26 Jun 2007 23:29:04 GMT

Does this mean you've already created a mirrored LVM?

I quote the man page for 'lvcreate' on my RHEL4 box:

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-m, --mirrors Mirrors
Creates a mirrored logical volume with "Mirrors" copies. For example, specifying "-m 1" would result in a mirror with two-sides; that is, a linear volume plus one copy.
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That being said, this is from the man page for 'lvextend':

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lvextend allows you to extend the size of a logical volume. Extension of snapshot logical volumes (see lvcreate(8) for information to create snapshots) is supported as well. But to change the number of copies in a mirrored logical volume use lvconvert(8).
------------------------------------

'lvconvert' has the exact same '-m' options as 'lvcreate'.

NOTE: As this is RHEL4, this is all LVM2. LVM1 does *NOT* have any Mirroring capabilities (unless using md over LVM).

Re: does the mirroring supported by LVM ( LINUX )

skt_skt — Wed, 27 Jun 2007 09:00:55 GMT

whihc update version you have with RHEL 4. I am not able to see the -m option for lvcreate too for both RHEL 3 and RHEL 4

Red Hat Enterprise Linux AS release 4 (Nahant Update 4);lvm2-2.02.06-6.0.RHEL4
Red Hat Enterprise Linux AS release 3 (Taroon Update 8);lvm-1.0.8-14

Re: does the mirroring supported by LVM ( LINUX )

Ivan Ferreira — Wed, 27 Jun 2007 09:05:03 GMT

I have Red Hat EL 4 U5 and we use LVM mirrors.

cat /etc/redhat-release
Red Hat Enterprise Linux ES release 4 (Nahant Update 5)

rpm -qi lvm2
Name : lvm2
Version : 2.02.21
Release : 5.el4

Re: does the mirroring supported by LVM ( LINUX )

Steven E. Protter — Wed, 27 Jun 2007 13:27:27 GMT

Shalom,

You still need to use fdisk to set up the partition structure on the second disk.

Its somewhat easier to do the mirroring at install time and do one gigantic partion and use lvm to subdivide it.

This methodology, which you can use to mirror a system after install seems quite possible as well using Stuart's plan.

This thread is so good its going on my permanent bookmark list in ITRC.

SEP

Re: does the mirroring supported by LVM ( LINUX )

skt_skt — Wed, 27 Jun 2007 20:45:28 GMT

Its somewhat easier to do the mirroring at install time and do one gigantic partion and use lvm to subdivide it.

I did not undesrtand this point.

This methodology, which you can use to mirror a system after install seems quite possible as well using Stuart's plan

r u talking about lvconvert/lvextend/lvcreate? Even i dont see a man page for lvconvert

Re: does the mirroring supported by LVM ( LINUX )

Stuart Browne — Wed, 27 Jun 2007 23:29:14 GMT

under RHEL4 with 'lvm2-2.02.21-5.el4', there most definately is a 'lvconvert' man page.

I personally feel tat using a whole-device for PE's is the easiest and most maintainable method of things.

That being said, after the fact 'lvconvert' into available PE's shouldn't be an issue.

Re: does the mirroring supported by LVM ( LINUX )

Van den Broeck Tijl — Thu, 28 Jun 2007 01:16:55 GMT

This "-m" option must have been added very recently or it's RH only.

I'm operating LVM2 v2.02.06 and it does not have a "-m" option.

That said, afaik (until this thread) the only way to mirror volumes is to use device mapper RAID support with a tool called 'mdadm' (which works pretty well, and it too can convert a running system on 1 disk live to a RAID 1 on 2 disks (presuming you already have the second disk installed or you've got hot-swap capabilities).

Off topic:
A difference between mdadm RAID 1 and LVM mirrors (such as in HP-UX) is that the linux device mapper utilises both disks for reading operations, resulting in a pretty good read performance whilst ie. HP-UX uses a single disk for read operations and the other only to write (until disk failure of first disk). I do not know how RH made the behaviour of the "-m" option in LVM, you still might be better using mdadm if you're looking for performance.

Re: does the mirroring supported by LVM ( LINUX )

Stuart Browne — Thu, 28 Jun 2007 03:47:07 GMT

Mirroring is one of the things that the Linux LVM developers have been trying to put in since it was first created.

When I initially started using LVM (albiet late, using a 1.0.3 version on FC1, with partial manual upgrads to 1.0.8), the documentation and notes were litted with people saying that it was being worked on, but not ready.

When LVM2 was released using device mapper support (ported back to 2.4 kernels), mirroring was added, but was quite buggy, and not in any of the man pages.

The documentation in the 'man' pages was added in 2.02.10.

If you read through the change log for LVM2 ( ftp://sources.redhat.com/pub/lvm2/WHATS_NEW ), you get quite the fascinating history.

Re: does the mirroring supported by LVM ( LINUX )

Van den Broeck Tijl — Thu, 28 Jun 2007 06:46:55 GMT

Thanks for the clarification Stuart. As far as I understand, it also uses md internally? Or am I totally wrong and it keeps mirrors in its own way?

Re: does the mirroring supported by LVM ( LINUX )

Ralph Grothe — Thu, 28 Jun 2007 08:21:39 GMT

As a resident of Berlin I really couldn't avoid to attend this year's "Linux Tag", which is said to be the biggest Linux event in Europe, and for the 1st time took place in my home town.
I followed almost all talks of the so called sysadmin track.
Among those there was one, which I found was one of the best talks held at this event, by Alasdair Kergon on "Clustered Volume Management on Fedora":

http://www.linuxtag.org/2007/en/conf/events/vortragsliste/details.html?talkid=72

This talk presented an unexpectedly deep view into the intricacies of cluster ready LVM performance and the sophisticated involved locking mechanism.

After the talk I also had the chance to have a few questions addressed personally to Alasdair in a small group of equally interested participants.

Because I also have long been awaiting RAID1 functionality to make it into the Linux LVM I asked if it already was available by now,
and whether it would be ready for production duty.
Especially the latter Alasdair hesitated to agree, and rather suggested that for the time being we stayed with Linux MD RAID, and used those as PVs for LVM.
That's the current state that we have on our Linux boxes, and so far we haven't had any bad experience with it.

Re: does the mirroring supported by LVM ( LINUX )

skt_skt — Tue, 03 Jul 2007 12:56:19 GMT

To be mentioned are

RHEL 4 update 5 supports LVM mirroe.
Then mdadm tool or the MD RAID

Thanks to all who ever participated