Running LVM on shared lun's
I have two systems that are connected to a SAN. The SAN is exporting the same 4 luns to each system (/dev/sd[b,c,d,e]). Under normal operation system1 will combine sdb with sdc into a vg and system2 will combine sdd with sde into a vg with both vgs consisting of one large lv and one small lv. After the system is configured there will be no modifications made to the LVM configuration. LVM is configured on one node and then copied over to the second node.
The million dollar question is, can system1 and system2 simultaneously have both of the VGs active without hosing any data?
I am not trying to have the same filesystem mounted simultaneously, just have the LVs available simultaneously for failover needs
I know that this sort of config can be done with the GFS pool volume manger but I have been told that many other VMs don't support this behavior....
Thanks,
Josh
Re: [linux-lvm] Running LVM on shared LUNs
Quoted 10 lines · Joshua Aune
I have two systems that are connected to a SAN. The SAN is exporting the same 4 luns to each system (/dev/sd[b,c,d,e]). Under normal operation system1 will combine sdb with sdc into a vg and system2 will combine sdd with sde into a vg with both vgs consisting of one large lv and one small lv. After the system is configured there will be no modifications made to the LVM configuration. LVM is configured on one node and then copied over to the second node.
The million dollar question is, can system1 and system2 simultaneously have both of the VGs active without hosing any data?
As I understand it, only if you are using a filesystem that supports clustered operations, like GFS.
Quoted 2 lines
I am not trying to have the same filesystem mounted simultaneously, just have the LVs available simultaneously for failover needs
In that case, as long as you have some heartbeat or something that lets you know when the one system needs to take over the other's PVs. The trick here is that if you lose your network connection, but the box is still accessing data on the LUNs, that could become problematic. Maybe a tiny little shared GFS thing would allow your boxes a place to write some status info (a custom "heartbeat", if you will) so that a network disconnect or other issue won't cause false alarms.
Probably best to just use GFS.
Quoted 3 lines
I know that this sort of config can be done with the GFS pool volume manger but I have been told that many other VMs don't support this behavior....
/me shrugs
Not sure about that as I don't have any SAN to play with :( . Never tried it.
Signature · 10 lines
Lamont R. Peterson <[email protected]> Founder [ http://blog.OpenBrainstem.net/peregrine/ ] GPG Key fingerprint: 0E35 93C5 4249 49F0 EC7B 4DDD BE46 4732 6460 CCB5 ___ ____ _ _ / _ \ _ __ ___ _ __ | __ ) _ __ __ _(_)_ __ ___| |_ ___ _ __ ___ | | | | '_ \ / _ \ '_ \| _ \| '__/ _` | | '_ \/ __| __/ _ \ '_ ` _ \ | |_| | |_) | __/ | | | |_) | | | (_| | | | | \__ \ || __/ | | | | | \___/| .__/ \___|_| |_|____/|_| \__,_|_|_| |_|___/\__\___|_| |_| |_| |_| Intelligent Open Source Software Engineering [ http://www.OpenBrainstem.net/ ]
Re: [linux-lvm] Running LVM on shared LUNs
Hi,
One way to take care of this would be to use clustering software such as HP's MC Service Guard. I'm assuming you want to make an HA cluster of some sort because you specified that both servers do not need to access the same FS simultaneously (in which case you'd want to use VXFS or GFS).
Using Service Guard, the FS in question is part of a cluster package, and it is mounted by the cluster package, and is thus not specified in the fstab.The mounting or unmounting of the FS is taken care of when the package switches from one server to another, thus bringing its FSes with it. The SAN LUNs are seen on both sides ofcourse, and the LVM config is copied to both sides as well, its just only active and mounted on one side at a time. This works very well.
-Christian
[email protected] wrote on 08.08.2006 08:50:36:
Quoted 9 lines · Joshua Aune
Quoted 8 lines
I have two systems that are connected to a SAN. The SAN is exporting the same 4 luns to each system (/dev/sd[b,c,d,e]). Under normal operation system1 will combine sdb with sdc into a vg and system2 will combine sdd with sde into a vg with both vgs consisting of one large lv and one small lv. After the system is configured there will be no modifications made to the LVM configuration. LVM is configured on one node and then copied over to the second node.
Quoted 4 lines
Quoted 2 lines
The million dollar question is, can system1 and system2 simultaneously have both of the VGs active without hosing any data?
As I understand it, only if you are using a filesystem that
supportsclustered
Quoted 3 lines
operations, like GFS.
Quoted 1 line
I am not trying to have the same filesystem mounted simultaneously,
just
Quoted 3 lines
Quoted 1 line
have the LVs available simultaneously for failover needs
In that case, as long as you have some heartbeat or something that lets
you
Quoted 1 line
know when the one system needs to take over the other's PVs. The trick
here
Quoted 1 line
is that if you lose your network connection, but the box is still
accessing
Quoted 1 line
data on the LUNs, that could become problematic. Maybe a tiny little
shared
Quoted 2 lines
GFS thing would allow your boxes a place to write some status info (a custom "heartbeat", if you will) so that a network disconnect or other
issue
Quoted 11 lines
won't cause false alarms.
Probably best to just use GFS.
Quoted 3 lines
I know that this sort of config can be done with the GFS pool volume manger but I have been told that many other VMs don't support this behavior....
/me shrugs
Not sure about that as I don't have any SAN to play with :( . Nevertried
it.
Quoted 17 lines
--
Lamont R. Peterson <[email protected]>
Founder [ http://blog.OpenBrainstem.net/peregrine/ ]
GPG Key fingerprint: 0E35 93C5 4249 49F0 EC7B 4DDD BE46 4732 6460 CCB5
___ ____ _ _/ _ \ _ __ ___ _ __ | __ ) _ __ __ _(_)_ __ ___| |_ ___ _ __ ___ | | | | '_ \ / _ \ '_ \| _ \| '__/ _` | | '_ \/ __| __/ _ \ '_ ` _ \ | |_| | |_) | __/ | | | |_) | | | (_| | | | | \__ \ || __/ | | | | | \___/| .__/ \___|_| |_|____/|_| \__,_|_|_| |_|___/\__\___|_| |_| |_||_| Intelligent Open Source Software Engineering
[ http://www.OpenBrainstem.net/ ]
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Re: [linux-lvm] Running LVM on shared LUNs
In reply to Lamont R. PetersonQuoted 3 lines · Lamont R. Peterson
Quoted 1 line
The million dollar question is, can system1 and system2
simultaneously
Quoted 1 line
have both of the VGs active without hosing any data?
^^ lvm metadata
Quoted 4 lines
As I understand it, only if you are using a filesystem that supports clustered operations, like GFS.
Just to be clear, I should be able to issue [lv|vg]change -ay on both systems simultaneously with no LVM corruption (data integrity will be maintained by not starting a filesystems on both nodes simultaneously) (as long as I don't start the filesystem on both nodes).
I would use something like GFS, but this is a HA setup for Lustre oss/mds nodes :)
Thanks again,
Josh
Don't think LVM is cluster aware. Doing so can potentially cause loss of LV's/data due to metadata corruption on the LVM level. -----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Joshua Aune
Sent: Monday, August 07, 2006 3:00 PM
To: LVM general discussion and development
Subject: [linux-lvm] Running LVM on shared lun's
I have two systems that are connected to a SAN. The SAN is exporting the same 4 luns to each system (/dev/sd[b,c,d,e]). Under normal operation system1 will combine sdb with sdc into a vg and system2 will combine sdd with sde into a vg with both vgs consisting of one large lv and one small lv. After the system is configured there will be no modifications made to the LVM configuration. LVM is configured on one node and then copied over to the second node.
The million dollar question is, can system1 and system2 simultaneously have both of the VGs active without hosing any data?
I am not trying to have the same filesystem mounted simultaneously, just have the LVs available simultaneously for failover needs
I know that this sort of config can be done with the GFS pool volume manger but I have been told that many other VMs don't support this behavior....
Thanks,
Josh
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Quoted 3 lines · David Chan
Don't think LVM is cluster aware. Doing so can potentially cause loss of LV's/data due to metadata corruption on the LVM level.
LVM2 supports cluster locking, either using internal locking which works with CMAN or GULM, or by using an external locking library that can be customized to work with every cluster software that supports locking of resources.
L.
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