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Two ISCSI initiators not seeing the same data on the array

Posted on 2012-08-11
Medium Priority
Last Modified: 2012-08-17
I have two Ubuntu servers connected to the same ISCSI array.  Everything appears fine and I'm able to read the contents of the array from either server.  However, if I write to the array from server A, Server B doesn't see the new files until I disconnect and reconnect to the array from Server B.

Please advise.
Question by:dorianit
LVL 56

Assisted Solution

andyalder earned 1000 total points
ID: 38283690
ou need to use a cluster filesystem, the one you are using has the file allocation table (inode list etc, call it what you  want) stored in RAM. You'll also need a distributed lock manager. GFS will do for Linux.

Author Comment

ID: 38283712
so it's currently ext3 or ext4.  You're saying I need a lock manager (GFS)?  Is ext3/4 okay?

thank you.

Accepted Solution

B_Denison earned 1000 total points
ID: 38283792
You are begging for data corruption doing this without the clustered file system mentioned by andyalder.  This is because both systems have read/write capability to the same storage, but have no way to communicate to each other about what they are writing to which addresses and it's entirely possible - even likely - that the last server to write to a given address over-writes what the other server put there.

A clustered file system will install software on both machines so that they can synchronize what addresses are being 'reserved' for writes to each server and not step on each other.
LVL 56

Expert Comment

ID: 38283807
EXT3/4 will not do, there's a list of cluster filesystems here - http://en.wikipedia.org/wiki/Shared_disk_file_system.

The DLM is in addition, I think there are two available for use with GFS. The DLM stops both servers opening the same file at the same time.
LVL 81

Expert Comment

ID: 38283844
Iscsi targets often are a one to one access.
One host can access the the target at a time. What is the iscsi device in use?
It should include awarding to that effect.
Iscsi sends scsi commands over ip and there is no way, as others pointed out, to have commands processed by node1 dispatched to node2.

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