Readme and Release notes for release 4.1.0.1 General Parallel File System Advanced Edition 4.1.0.1 GPFS_ADV-4.1.0.1-power-Linux Readme

During internal testing, a rare but potentially serious problem has been discovered in GPFS. Under certain conditions, a read from a cached block in the GPFS pagepool may return incorrect data which is not detected by GPFS. The issue is corrected in GPFS 3.3.0.5 (APAR IZ70396). All prior versions of GPFS are affected.

The issue has been discovered during internal testing, where an MPI-IO application was employed to generate a synthetic workload. IBM is not aware of any occurrences of this issue in customer environments or under any other circumstances. Since the issue is specific to accessing cached data, it does not affect applications using DirectIO (the IO mechanism that bypasses file system cache, used primarily by databases, such as DB2® or Oracle).

This issue is limited to the following conditions:

1. The workload consists of a mixture of writes and reads, to file offsets that do not fall on the GPFS file system block boundaries;
2. The IO pattern is a mixture of sequential and random accesses to the same set of blocks, with the random accesses occurring on offsets not aligned on the file system block boundaries; and
3. The active set of data blocks is small enough to fit entirely in the GPFS pagepool.

The issue is caused by a race between an application IO thread doing a read from a partially filled block (such a block may be created by an earlier write to an odd offset within the block), and a GPFS prefetch thread trying to convert the same block into a fully filled one, by reading in the missing data, in anticipation of a future full-block read. Due to insufficient synchronization between the two threads, the application reader thread may read data that had been partially overwritten with the content found at a different offset within the same block. The issue is transient in nature: the next read from the same location will return correct data. The issue is limited to a single node; other nodes reading from the same file would be unaffected.

Follow the steps below to install the fix package:

1. Unzip and extract the update package (&lt filename >.tar.gz file) with one of the following commands:
   
   gzip -d -c &lt filename >.tar.gz | tar -xvf -
   
   or
   
   tar -xzvf &lt filename >.tar.gz


The list of RPM images in this directory should now be:

Required packages
The following packages are required for SLES and RHEL Linux:

gpfs.base-4.1.0-1.ppc64.update.rpm
gpfs.gpl-4.1.0-1.noarch.rpm
gpfs.docs-4.1.0-1.noarch.rpm
gpfs.msg.en_US-4.1.0-1.noarch.rpm
gpfs.ext-4.1.0-1.ppc64.update.rpm (GPFS Standard Edition and GPFS Advanced Edition only)
gpfs.crypto-4.1.0-1.ppc64.update.rpm (GPFS Advanced Edition only)

Optional packages
The following package is optional for SLES and RHEL Linux:

gpfs.docs-4.1.0-1.noarch.rpm

2. Follow the installation and migration instructions in your GPFS Concepts, Planning and Installation Guide (http://www-01.ibm.com/support/knowledgecenter/SSFKCN/gpfs_welcome.html).

In the below instructions, node-by-node upgrade cannot be used to migrate from GPFS 3.4 or prior releases. For example, upgrading from 3.4.x.x to 4.1.y.y requires complete cluster shutdown, upgrade install on all nodes and then cluster startup.

Upgrading GPFS may be accomplished by either upgrading one node in the cluster at a time or by upgrading all nodes in the cluster at once. When upgrading GPFS one node at a time, the below steps are performed on each node in the cluster in a sequential manner. When upgrading the entire cluster at once, GPFS must be shutdown on all nodes in the cluster prior to upgrading.

When upgrading nodes one at a time, you may need to plan the order of nodes to upgrade. Verify that stopping each particular machine does not cause quorum to be lost or that an NSD server might be the last server for some disks. Upgrade the quorum and manager nodes first. When upgrading the quorum nodes, upgrade the cluster manager last to avoid unnecessary cluster failover and election of new cluster managers.

1. Prior to upgrading GPFS on a node, all applications that depend on GPFS (e.g. DB2) must be stopped. Any GPFS file systems that are NFS exported must be unexported prior to unmounting GPFS file systems.
    
2. Stop GPFS on the node. Verify that the GPFS daemon has terminated and that the kernel extensions have been unloaded (mmfsenv -u). If the command mmfsenv -u reports that it cannot unload the kernel extensions because they are "busy", then the install can proceed, but the node must be rebooted after the install. By "busy" this means that some process has a "current directory" in some GPFS filesystem directory or has an open file descriptor. The freeware program lsof can identify the process and the process can then be killed. Retry mmfsenv -u and if that succeeds then a reboot of the node can be avoided.
   
   
3. Upgrade GPFS using the RPM command as follows(make sure to be in the same directory as the files):
   
   For SLES or RHEL system,
   rpm -Uvh gpfs*.rpm
   



4. Recompile any GPFS portability layer modules you may have previously compiled. The recompilation and installation procedure is outlined in the following file:
   
   /usr/lpp/mmfs/src/README

The update images listed below and contained in the tar image with this README are maintenance packages for GPFS. The update images are a mix of standard RPM images that can be directly applied to your system.

The update images require a prior level of GPFS. Thus, the usefulness of this update is limited to installations that already have the GPFS product. Contact your IBM representative if you desire to purchase a fully installable product that does not require a prior level of GPFS.

After all RPMs are installed, you have successfully updated your GPFS product.

Before installing GPFS, it is necessary to verify that you have the correct levels of the prerequisite software installed on each node in the cluster. If the correct level of prerequisite software is not installed, see the appropriate installation manual before proceeding with your GPFS installation.

For the most up-to-date list of prerequisite software, see the GPFS FAQ in the IBM® Knowledge Center (http://www-01.ibm.com/support/knowledgecenter/SSFKCN/gpfs_welcome.html)

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