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not able to mount shared lun partiton on rhel 5

Posted on 2016-08-04
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Last Modified: 2016-08-06
Hi All,

Here is my situation:

i have an shared Lun from storage i dont know how they are sharing. Its of 4 TB so fdisk not working.

I have formatted it using parted tool successfully. but issue is when i formatted on one machine i am able to mount and use it.

but at same time when i try same on another server - i am able to see that disk but even partiton in fdisk but it says special device mount not possible .

now if i again format it on second machine i am able to mount but then another giving issues and every time data loss is there.

I know something silly i am doing but please help me in this.

Here what I need:

RHEL 5.5 and have 4 TB LUN Shared LUN from storage.

I want it to use on both server as a mount point.

please help me with right approach.

Thank you
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Question by:The Rock
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by:Gerald Connolly
Gerald Connolly earned 250 total points
ID: 41743711
Ah the old shared LUN conundrum!

The problem with shared LUN's with multiple writers (sharing with only one writer is OK) is that if one system writes to a block and then another system writes to the same block, only the second update will actually be on Disk, this isnt good, especially if those blocks are part of the file system e.g directory.

So if you require multiple writers you need a Lock-Manager to control who writes what and when. The Lock-Manager is normally via a clustered File system eg for RHEL GFS
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robocat earned 250 total points
ID: 41743717
What exactly do you mean by "shared" LUN?

You can never mount a LUN on more than one system at the same time unless you use a clustered filesystem. Do you use a clustered filesystem?

If you're simply trying to share files amongst different servers, you need a completely different approach by exporting the filesystem as NFS and mounting the NFS share on the second server. Or perhaps the storage box can provide an NFS share instead of a LUN, which makes this even simpler.
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by:Gerald Connolly
ID: 41743737
Using a shared LUN without a Clustered File System will end in tears (and serious Filesystem and Data corruption)
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Author Comment

by:The Rock
ID: 41743777
Hi All,


Thank you for your comments and agree with all of you but the problem is previously it was working fine with the same settings without any cluster or tool . the only diffrence was size and command.

Like previosuly size was 1.2 TB and we have used fdisk to create partition and now size is 4 TB and tool is parted.  since we have used parted tool to format and create partiton this issue occured.
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Author Comment

by:The Rock
ID: 41743793
Another thing i am able to see the partiton in fdisk -l and fdisk tool like /dev/sdd1 but when i am fidning it in /dev its not there
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by:robocat
ID: 41744047
You might think it worked, but data corruption and data loss is inevitable sooner or later.

Don't even try to make this work without a clustered file system. Or use NFS as an alternative.
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Expert Comment

by:Gerald Connolly
ID: 41744076
Thank you for your comments and agree with all of you but the problem is previously it was working fine with the same settings without any cluster or tool . the only diffrence was size and command.

Trust us! If you were using a shared LUN and/or partition with both systems able to write all you were going to get is a Corrupt filesystem and Corrupt data. It is possible to setup a shared LUN that is mounted Read/Write on one system and Read-Only on the other and that will work fine without cluster software, but if both systems want to write to the same bit of disk then a clustered file-system is MANDATORY!
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Author Comment

by:The Rock
ID: 41745628
Hi all thank u so much for your suggestion . As I said I agree with your recommendation but end we all know it's depend on customer what he wants. Finally I found the way by creating only partition on second server using parted tool for sdd and it works even data also not destroyed .

Thanks again to all
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