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Physical vs Logical Blocksize on ASMLib Devices

As you all may know, ASMLib is a recommended module for Oracle databases running on Linux platforms and it is an embedded module for UEK (Oracle Unbreakable Kernel) users. Oracle announced that (two years ago or so) they will no longer maintain ASMLib for Red Hat compatible kernel but this does not mean that they abandon the project, rather it is mainly related to the effort they need to put in maintaining the module for multiple kernel versions.

A while ago, Oracle added a new feature to ASMLib allowing ASM devices to choose between physical or logical block sizes in I/O operations. This should be, I believe, a fail-back mechanism for SSD devices used as ASM disks. Many SSD devices use 4K block size however Linux still uses default 512 bytes logical block size for those devices in the same way it does for motor disks. In early releases of ASMLib (oracleasm-support-2.1.7 and earlier), ASM uses physical block size (4K for SSDs). This is still the default behavior in oracleasm-support-2.1.8 but now sysadmin can choose between physical and logical blocksize by using [-b|-p] switches in script.

  • -b|—logical-blocks sets logical blocksize usage
  • -p|—physical-blocks set physical blocksize usage

Those switches set /sys/module/oracleasm/parameters/use_logical_block_size which is default to be false (use physical blocksize). So that asmlib module can use the value to decide which block size to use.

VMware Tools for Oracle UEK

If you wish to use VMware Tools with Oracle UEK as the guest OS (you should use it in order to interact guest with the host, proper screen resolution and many other functionality) you need to perform some extra steps unlike some other Linux distros. Such as Ubuntu, which can be automatically configured by VMware

Here is the list of actions you should take for installation:

  1. Configure yum on your Linux installation
  2. Using VMware Virtual Machine menu choose Install VMware Tools option which will mount a pseudo device.
  3. Copy VMwareTools-8.8.4-730257.tar.gz  into /tmp and extract it using tar -xzvf VMwareTools-8.8.4-730257.tar.gz 
  4. yum install kernel-headers kernel-uek-devel
  5. ./ as root

You are done.