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Re: [Linux-cluster] Data Loss / Files and Folders "2-Node_GFS-Cluster"



Doug Tucker wrote:
I don't (or "didn't") have adequate involvements with RHEL5 GFS. I may not know enough to response. However, users should be aware of ...

Before RHEL 5.1 and community version 2.6.22 kernels, NFS locks (i.e. flock, posix lock, etc) is not populated into filesystem layer. It only reaches Linux VFS layer (local to one particular server). If your file access needs to get synchronized via either flock or posix locks *between multiple hosts (i.e. NFS servers)*, data loss could occur. Newer versions of RHEL and 2.6.22-and-above kernels should have the code to support this new feature.

There was an old write-up in section 4.1 of "http://people.redhat.com/wcheng/Project/nfs.htm"; about this issue.

-- Wendy

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Wendy,

To be clear, does this include RHEL 4.7, or is it specific to 5.x?

The changes were made on 2.6.22 kernel. I would think RHEL 4.7 has the same issue - but I'm not sure as I left Red Hat before 4.7 was released. Better to open a service ticket to Red Hat if you need the fix.

If applications are directly run on GFS nodes, instead of going thru NFS servers, posix locks and flocks should work *fine* across different nodes. The problem had existed in Linux NFS servers for years - no one seemed to complain about it until clusters started to get deployed more commonly.

-- Wendy


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