[IQUG] What is the IQ performance penalty from using file systems in Linux kernel version 2.6 and above?

Ron Watkins rwatkins at dssolutions.com
Wed Jul 4 13:02:26 MST 2018


You can continue to use RAW devices under RHEL, and RHEL 7.4 still supports
ext4 filesystems also.

Performance is generally dictated by the storage itself, and is less
dependent on the "format" of the storage.

Thus, if you have multiple disks providing multiple paths to storage you
will see a greater improvement over a single disk.

RAW devices do perform better than filesystem, however, it's not possible to
put an exact value on how much better as they are both strongly dependent on
the underlying storage.

Ron

 

From: iqug-bounces at iqug.org [mailto:iqug-bounces at iqug.org] On Behalf Of
Steve Shen
Sent: Wednesday, July 04, 2018 12:15 PM
To: iqug at iqug.org
Subject: [IQUG] What is the IQ performance penalty from using file systems
in Linux kernel version 2.6 and above?

 

Today's Topic:

 

(1). What is the IQ performance penalty from using file systems relative to
using true raw partitions for main store and temporary store in Linux kernel
version 2.6 and above?

 

We are considering to migrate our IQ Simplex from Solaris X64 to RedHat
version 6.8 or 7.4. They are Linux kernel version 2.6 and above.  

 

RedHat version 6.8 uses "ext4" file system.  RedHat version 7.4 used "xfs"
file system.

 

This discussion is for IQ Simplex only.  I am very aware that using file
systems will prevent me from converting the Simplex to Multiplex later.

 

Based on the documentation below, it seemed okay in using file systems at
Linux kernel version 2.6 and above:

 

http://infocenter.sybase.com/help/topic/com.sybase.infocenter.dc00169.1600/d
oc/pdf/iqperf.pdf

"

Controlling File System Buffering

On some file systems, you can turn file system buffering on or off. Turning
file system

buffering off usually reduces paging and improves performance.

To disable file system buffering for IQ Main dbspaces of existing databases,
issue the

following statement:

SET OPTION "PUBLIC".OS_FILE_CACHE_BUFFERING = OFF

To disable file system buffering for IQ Temporary dbspaces of existing
databases, issue the

following statement:

SET OPTION "PUBLIC".OS_FILE_CACHE_BUFFERING_TEMPDB = OFF

You can only set this option for the PUBLIC role. Shut down the database and
restart it for the

change to take effect.

This direct I/O performance option is available on Solaris UFS, Linux, Linux
IBM, AIX, and

Windows file systems only. This option has no effect on HP-UX and HP-UXi and
does not

affect databases on raw disk. In Linux, direct I/O is supported in kernel
versions 2.6.x

To enable direct I/O on Linux kernel version 2.6 and AIX, also set the
environment variable

IQ_USE_DIRECTIO to 1. Direct I/O is disabled by default in Linux kernel
version 2.6 and

AIX. IQ_USE_DIRECTIO has no effect on Solaris and Windows.

"

 

It's also documented by Mark that using file systems is normally slower than
true raw partitions in Linux:

 

https://archive.sap.com/discussions/thread/3518966

 

Did any of us ever do apple-to-apple comparisons and measure the performance
penalty relative to using true raw partitions?

 

Was it 5%, 10%, 15% or 20% performance penalty or more from using file
systems instead of true raw partitions at Linux?

 

Thank you.

 

Happy Independency Day!

Steve Shen

SS&C Technologies

 

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