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Re: shared LVM

 
Rick Tweedy_1
Occasional Contributor

shared LVM

Hi all,

I was surprised to see similiar messages relating to the exact thing I am working on. We too do not use Lock manager and/or service gaurd. Why? Well it is not a failover system. We want our t600 and our n4000 to share disk on a huge array via fiber to alow for fast file movement between the systems.

I did the exact list of steps listed in one of the responses here. (ie, vgexport map, ftp, vgimport etc). the bizzare thing is on system b(with read only access) the FS does not seem to get updated unless I unmount and re-mount. I have try the various sync commands with no luck.

What really confuses me is that it would seem to me that this requirement of sharing disk space via fibre and two machines is not that rare of a request yet HP does not seem to be able to give me any clear direction as to the most reliable(ie right) way of doing it. We basically need the space as a temp dumping ground for HUGE flat files for the other system to pick up. It sounds like we are in for alot of management and very light treading in this type of uncontrolled environment...possibly sys admins nightmare? I would love to hear of any experiences others may have had with this type of situation.

Thanks
Rick Tweedy
Shared LVM
5 REPLIES 5
Manju Kampli
Trusted Contributor

Re: shared LVM

if you are using EMC, there is a option for BCVs. This does the alomost same function as lvsplit and lvsync with in EMC. you can sync these BCVs to the disks you want to copy and split it and mount these disks on the systems where you want to copy the data.
Never stop "LEARNING"
Anthony Goonetilleke
Esteemed Contributor

Re: shared LVM

It is a big NO NO do do this the way you are doing it and you could end up with corrupted disks very easily unless you use things like lockmanager etc.
If you are using a EMC symmetrix they do have a product that acts almost like a NFS server that sits on the symmetrix box so that you get the speed of fibre although you mount it as if it is a NFS volume. I am pretty sure it supports most Unix flavours and NT.
Minimum effort maximum output!
Stefan Stechemesser
Honored Contributor

Re: shared LVM

Perhaps you should think about a Gigabit lan connection between the two computers and use NFS to share files (fibrechannel: 1063 Mbit/sec). The advantage of the direct fibrechannel connection to the diskarray is redundency which you don't have with the NFS solution.
Jim Mulshine
Frequent Advisor

Re: shared LVM

I have done something like what you are describing. We had two N-Class with ServiceGuard and two K-Class with ServiceGuard, that is, two separate clusters.
One day I wanted to run a database on the N-Class, a database which normally runs on the K-Class cluster. Since the N and K machines were all connected physically to the same FiberChannel network and the same disk arrays, I could use that vgexport map, ftp, vgimport, vgchange technique to access the database from an N-Class. I think the difference here is that I accessed the database from only one machine at a time, being very careful not to enable the volume group on more than one machine. Actually I did try enabling the volume group on two machines at the same time just to see if it worked, but I did not do anything with the files under this time.

I suppose you could make a script that automates switching the volume group over to the other machine and vice versa. Then machine A could put its files on the vg, you perform the switch, and machine B could access the files. I think that would be pretty safe. I would make sure both machines had the same OS and filesystem versions first.
JUP
Regular Advisor

Re: shared LVM

Hi Rick,
Your situation is different to mine in that you seem to have both systems up and running accessing the same LVM. In my case I had one system mounting the data and the second system as standby. Once the main system falls over, the standby will then start up, mount the data drive and then continue working. Since I mounted the drive when I required it I was always able to get the latest info from the disk. In your case, it sounds that data corruption is very possible where both systems mount the drive.