When troubleshooting performance problems, be aware that SAS processes place different demands on file systems and I/O than traditional databases or simple query processes. For that reason, you need to be able to determine the throughput rates of any file system that SAS uses. This paper documents a shell script that system administrators and IT teams can use to help make that determination.

The rhel_iotest.sh script

The rhel_iotest.sh script is an automated utility that uses UNIX/Linux dd commands to measure the I/O throughput of a file system in a Red Hat Enterprise Linux (RHEL) environment. This method mimics the behavior of SAS. The results should give you a reasonable estimate of I/O throughput, but might not reflect the actual performance of SAS applications.

Utility Deployment from the SAS Technical Support Sample Tools (SASTSST) Repository

To deploy the utility from the SASTSST repository, complete the following steps when you are logged on to your problematic server using the SAS installer user ID:

1. Click the Downloads tab in this note to download the SASTSST_UNIX_installation.sh utility.
2. Execute the bash SASTSST_UNIX_installation.sh utility.
3. Review and accept the license terms and conditions.
4. When prompted, provide an absolute path to a deployment directory (such as /usr/local/etc/SAS/) to define the location for your SAS Technical Support Sample Tools.
5. Select the Testing Throughput for your SAS 9 File Systems: RHEL Linux platforms option. After the utility is deployed, you see the following content in your deployment directory:

     6. Make the rhel_iotest.sh file executable (chmod 0555 rhel_iotest.sh). The script is now ready to use.

Usage

The rhel_iotest.sh utility evaluates your RHEL environment, calculates all required parameters based on your system’s specifications, and launches a series of Write and Read tests. The utility then compiles all files from the tests into a file called rhel_iotest_[hostname]_[date]-[time].tar.gz. This tarball contains a copy of the script, its log, results files, and the contents of 2 system files: /proc/cpuinfo and /proc/meminfo.

Execute the test script from a file system separate from the target file system that you are testing.For accurate results, your target file system must have free space greater than (the number of physical cores in your system) * (the amount of physical RAM in your system).

The shell script is parameter-driven:

   ./rhel_iotest.sh -t <target file system>

where -t is the file system you want to test.

The script produces output to the screen in addition to the resulting tarball. The example below demonstrates the output of a command where the file system being tested is /saswork:

RESULTS
-------

INVOCATION:  rhel_iotest -t /saswork
 

TARGET DETAILS
  directory:    /saswork
  df -k:        /dev/mapper/vg_saswork 4183836672 33824 4183802848   1% /saswork
  mount point:  /dev/mapper/vg_saswork on /saswork type xfs (rw,noatime,nodiratime)
  filesize:     251.47 gigabytes

 

STATISTICS
  read throughput rate:     394.30 megabytes/second per physical core
  write throughput rate:    392.26 megabytes/second per physical core

In the example above, you can see that the average Read throughput rate is about 394 MB/second.
The average Write throughput rate is about 392 MB/second.

What Should You Expect to See?

The I/O throughput requirements for the SAS Compute tier are as follows:

• For the WORK/UTILLOC file system, SAS requires a minimum I/O throughput rate of 125 MB/second per physical CPU core.
• For permanent SAS data files, SAS requires a minimum I/O throughput rate of 75-100 MB/second per physical CPU core.
• Overall, I/O throughput should be, at minimum, 100-125 MB/second per physical CPU core.

Consult with your storage administration team regarding how to achieve adequate throughput based on these general guidelines.

There are several papers available that will help you understand how SAS performs I/O, as well as minimum I/O recommendations for SAS file systems. These papers outline the recommended I/O metrics for file systems that support SAS deployments, and they identify guidelines that can help with provisioning and tuning I/O characteristics for optimal SAS performance. You can access these papers via SAS Note 42197, "Tuning guidelines and best practices for your hardware infrastructure (systems, storage, virtualization, file systems, and operating systems)."

• Best Practices for Configuring your IO Subsystem for SAS 9 Applications
• Frequently Asked Questions Regarding Storage Configurations
• How to Maintain Happy SAS 9 Users

For minimum CPU and RAM requirements, refer to System Requirements for SAS® 9.4 Foundation for Linux for x64.

Note: For best performance of SAS in RHEL environments, ensure that you have followed the guidance in Optimizing SAS on Red Hat Enterprise Linux (RHEL) 6 & 7.

Non-RHEL environments

To test I/O throughput rates for file systems in AIX, HPI, and Oracle Solaris environments, use the iotest.sh script, documented in SAS Note 51660.

Operating System and Release Information

Product Family	Product	System	SAS Release
			Reported	Fixed*
SAS System	Base SAS	Linux for x64

* For software releases that are not yet generally available, the Fixed Release is the software release in which the problem is planned to be fixed.

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SASTSST_UNIX_installation.sh

This SAS Note documents the rhel_iotest.sh script, an automated utility that uses UNIX/Linux dd commands to measure the I/O behavior of a Red Hat Enterprise Linux (RHEL) environment.

Type:	Usage Note
Priority:

Date Modified:	2023-03-31 11:28:57
Date Created:	2017-01-12 19:05:57