I've never been the biggest fan of Oracle ASMLib. While it is far easier to configure disks for ASM using ASMLib than udev or multipath, it also added an additional requirement for rpms, an additional layer in the stack, and dependency on the kernel version. An internet search will reveal numerious discussions on this very topic, with many having a preference to not use ASMLib. However, due to the increased ease of configuration, strong recommendations from Oracle and believed performance improvements I had always used ASMLib. For what it's worth, there does seem to be some truth behind ASMLib having a performance benefit as though I've not personally tested it, I have read blog postings where its removal resulted in greater CPU usage. If you have enough resources this is not a major concern though over time it may end of being the case.
My stance, and I would think a lot of others, have since changed with the recent developments in Oracle's competition with Red Hat. To be more specific, MOS note "Oracle ASMLib Software Update Policy for Red Hat Enterprise Linux Supportd by Red Hat [ID 1089399.1]", the quote of interest being:
"For RHEL6, Oracle will only provide ASMLib software and updates when configured with a kernel distributed by Oracle. Oracle will not provide ASMLib packages for kernels distributed by Red Hat as part of RHEL6. ASMLib updates will be delivered via Unbreakable Linux Network(ULN) which is available to customers with Oracle Linux support. ULN works with both Oracle Linux or Red Hat Linux installations, but ASMlib usage will require replacing any Red Hat kernel with a kernel provided by Oracle."
With this note, I've since been devoting time to updating my Oracle database standards for Linux, i.e. SLES and RHEL since we are not an Oracle Linux shop and have no plans to pursue such a course (nothing personal Oracle, it's just business). So I began work on what I though was simply making a few modifications to use udev instead of ASMLib following which I'd do due diligence to test it out on our standard versions of SLES and RHEL. I've used it before on RHEL and it should prove simple enough, right?
The Case of the Missing SCSI ID
I was so wrong. When I tried to obtain the SCSI ID for the disks during my testing nothing was returned. I spent some time researching, but came up empty until I realized I was not searching correctly. You see we now run most of our Linux environments on VMware vSphere and I was not using this in my search terms. Correct input and bingo! Seems there is a known issue where by default VMware does not expose SCSI IDs for the disks. To correct this you will need to:
- Shutdown your VM guest
- In vCenter, right click your VM guest in the LHS pane and select 'Edit Settings...' (can also be obtained directly via 'Summary' tab)
- Click the 'Options' tab
- Select the 'Advanced -> General' navigation item on the left side and click the 'Configuration Parameters...' button displayed on the right
- Click the 'Add Row' button
- Add the name 'disk.EnabledUUID' with a value of 'TRUE' (no quotes of any kind) and click 'OK' all the way through the screens to save
- Restart your VM guest and enjoy receiving SCSI IDs
UDEV Steps
Now onwards with the steps for udev configuration!
1. Add the "options=-g" line to the /etc/scsi_id.config file as the root user.
2. Obtain the SCSI ID for your disks as the root user:
/sbin/scsi_id -g -s /block/{sd_device}
3. Create a udev rules file in /etc/udev/rules.d directory as the root user with entries similar to the below:
vi /etc/udev/rules.d/99-udev-oracle.rules
# ####################################################
# FILE: 99-udev-oracle.rules
# DESC: UDEV rules file for Oracle ASM functionality.
# Should be placed under /etc/udev/rules.d
# ####################################################
# DATA disks
KERNEL=="sd*",BUS=="scsi",ENV{ID_SERIAL}=="{scsi_id}
# FRA disks
KERNEL=="sd*",BUS=="scsi",ENV{ID_SERIAL}=="{scsi_id}
4. Stop and start udev as the root user:
/etc/init.d/boot.udev stop
/etc/init.d/boot.udev start
The SCSI devices can now be accessed by ASM, and you can set your ASM_DISKSTRING parameter to be "/dev/asmdisk*".
