[IQUG] IQUG Digest, Vol 67, Issue 8

Steve Shen sshen at sscinc.com
Fri Jul 6 05:59:26 MST 2018


Today's Topics:

   1. Re: IQUG Digest, Vol 67, Issue 5 (Mumy, Mark)
   2. Re: IQUG Digest, Vol 67, Issue 5 (Steve Shen)
   3. Re: ext3 or ext4 or xfs in Linux (Steve Shen)

I am adding item #3 above for today's discussion.

The default file systems at Red Hat version 6.8 and Red Hat version 7.4 were ext4 and xfs respectively in my company.

Based on my understanding, ext4 is superior to ext3 and xfs is superior to ext4 in general.

The file system  ext4 allows us to disable journaling to make the file systems perform better.  Is this a common practice to disable journaling in IQ? Will we lose recovery due to turning off journaling?

Was there a consensus in this IQ community how to determine to use ext3 or ext4 or xfs for any of the following stores?
1.  IQ Simplex catalog store;
2. IQ Simpelx data store;
3. IQ Simplex temp store;
4. IQ backup file system;

Notes: We are going to use SnapMirror from the primary IQ machine to the DR host.

Please let me know if you have the answers.  Thank you.

Regards,

Steve Shen

-----Original Message-----
From: iqug-bounces at iqug.org [mailto:iqug-bounces at iqug.org] On Behalf Of iqug-request at iqug.org
Sent: Thursday, July 05, 2018 12:41 PM
To: iqug at iqug.org
Subject: IQUG Digest, Vol 67, Issue 8

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Today's Topics:

   1. Re: IQUG Digest, Vol 67, Issue 5 (Mumy, Mark)
   2. Re: IQUG Digest, Vol 67, Issue 5 (Steve Shen)


----------------------------------------------------------------------

Message: 1
Date: Thu, 5 Jul 2018 16:26:16 +0000
From: "Mumy, Mark" <mark.mumy at sap.com>
To: Steve Shen <sshen at sscinc.com>, "iqug at iqug.org" <iqug at iqug.org>
Subject: Re: [IQUG] IQUG Digest, Vol 67, Issue 5
Message-ID: <51C29F4D-3DDD-4A37-B14B-CF9A82D3081B at sap.com>
Content-Type: text/plain; charset="utf-8"

Just saw your questions on RHEL versions.

See my other email....  Using the manuals from Sybase.com isn't advised as they are not kept up.  For platform specific stuff and OS certifications, you can only get the currently supported platforms from sap.com, here.  What we list in the manuals was the initial versions supported.  We don't update the manuals when we test newer OS versions, we always update the SAP PAM (product availability matrix).
https://apps.support.sap.com/sap(bD1lbiZjPTAwMQ==)/support/pam/pam.html?smpsrv=https%3a%2f%2fwebsmp106.sap-ag.de#ts=0

See the IQ 16 manual you point to is grossly out of date and only shows RHEL 5 and 6 as supported when the products were first released.  Use the above link and you will see that other versions are included as well.  That link also includes other platform related details that are important for IQ deployment on various platforms.  Here's the link to all Linux versions supported for IQ 16.0:
https://apps.support.sap.com/sap/support/pam?hash=s%3D%26filter%3Dfavorites%257CT%26o%3Dmost_viewed%257Cdesc%26st%3Dl%26rpp%3D20%26page%3D1%26pvnr%3D67838200100900005877%26pt%3Dt%257COS%26fclfilter%3DG1%257CLINUX%2520ON%2520X86_64%26ainstnr%3D67838200104900016656

Our support for OS versions is a tad relaxed.  If it says RHEL 6.2, that doesn?t mean it?s the only version we support.  That's the minimum version we support for the main release of RHEL 6.  Our policy is to support any of the dot releases at that or a higher level.  So not RHEL 6.2, but really RHEL 6.2+ or RHEL 6.x with a minimum of 6.2.  However you want to read it.

With IQ 15.4, you can use whatever OS you want without fear of violating support.  OK, it's not quite THAT easy.  IQ 15.4 is no longer supported.  So any OS that you want to support would be just fine.

Do you have an SAP S-number?  The SAP sites contain quite a lot of details on IQ deployments in the PAM, roadmaps, SAP Notes, and manuals.

Mark

Mark Mumy
Strategic Technology Incubation Group
SAP Global Center of Excellence |  SAP
M +1 347-820-2136 | E mark.mumy at sap.com
My Blogs: https://blogs.sap.com/author/markmumy/

https://sap.na.pgiconnect.com/I825063
Conference tel: 18663127353,,8035340905#

?On 7/5/18, 11:03 AM, "iqug-bounces at iqug.org on behalf of Steve Shen" <iqug-bounces at iqug.org on behalf of sshen at sscinc.com> wrote:

    Today's Topics:

    1. Re: What is the IQ performance penalty from using file
          systems in Linux kernel version 2.6 and above? (Steve Shen)

    2. Re: RedHat Enterprise Linux versions for IQ versions 15.4 and 16.0 (Steve Shen)

    The following are for IQ 15.4 and 16.0 at Linux from the document link http://infocenter.sybase.com/help/topic/com.sybase.infocenter.dc10083.1540/doc/pdf/iqicglin.pdf and http://infocenter.sybase.com/help/topic/com.sybase.infocenter.dc10083.1600/doc/pdf/iqicglin.pdf

    "
    Supported Server Platforms
    Sybase IQ is compatible with these platforms and operating systems.
    * Red Hat Enterprise Linux 6.2 (Linux on POWER; 64-bit)
    * Red Hat Enterprise Linux 6.2 x86-64, Advanced Server and Workstation Editions
    * Red Hat Enterprise Linux 6.0 (Linux onPOWER;64-bit) - minimum patch level Update-2
    * Red Hat Enterprise Linux 6.0 x86-64, Advanced Server and Workstation Editions -
    minimum patch level Update-2
    * Red Hat Enterprise Linux 5.5 (Linux onPOWER;64-bit) - minimum patch level Update-2
    * Red Hat Enterprise Linux 5.5 x86-64, Advanced Server and Workstation Editions -
    minimum patch level Update-2
    * SuSE Linux Enterprise Server (SLES) 11.0 x86-64 - minimum patch level SP1
    * SuSE Linux Enterprise Server (SLES) 11.0 (Linux on POWER; 64-bit) - minimum patch
    level SP1
    Supported Client
    "
    Red Hat Enterprise Linux 5.5 x86-64 or 6.0 x86-64 or 6.2 x86-64 are very old.

    Can I used Red Hat Enterprise Linux version 6.8 or 7.4?  Please advise.  Thank you.

    Regards,

    Steve

    -----Original Message-----
    From: iqug-bounces at iqug.org [mailto:iqug-bounces at iqug.org] On Behalf Of iqug-request at iqug.org
    Sent: Thursday, July 05, 2018 11:42 AM
    To: iqug at iqug.org
    Subject: IQUG Digest, Vol 67, Issue 5

    Send IQUG mailing list submissions to
            iqug at iqug.org

    To subscribe or unsubscribe via the World Wide Web, visit
            http://iqug.org/mailman/listinfo/iqug
    or, via email, send a message with subject or body 'help' to
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            iqug-owner at iqug.org

    When replying, please edit your Subject line so it is more specific than "Re: Contents of IQUG digest..."


    Today's Topics:

       1. Re: What is the IQ performance penalty from using file
          systems in Linux kernel version 2.6 and above? (Steve Shen)


    ----------------------------------------------------------------------

    Message: 1
    Date: Thu, 5 Jul 2018 15:41:43 +0000
    From: Steve Shen <sshen at sscinc.com>
    To: "'Mumy, Mark'" <mark.mumy at sap.com>, Ron Watkins
            <rwatkins at dssolutions.com>, "Baker, Chris" <c.baker at sap.com>,
            "iqug at iqug.org" <iqug at iqug.org>
    Subject: Re: [IQUG] What is the IQ performance penalty from using file
            systems in Linux kernel version 2.6 and above?
    Message-ID:
            <0C03FF7E7FA66E41A61525750FD653399DC52633 at ykt1emxprd6.globeop.com>
    Content-Type: text/plain; charset="utf-8"

    Hi Mark,

    The senior management had chosen ?ease? over ?performance?.

    Thank you very much for your feedback.

    Regards,
    Steve
    From: Mumy, Mark [mailto:mark.mumy at sap.com]
    Sent: Thursday, July 05, 2018 11:10 AM
    To: Ron Watkins; Baker, Chris; Steve Shen; iqug at iqug.org
    Subject: Re: [IQUG] What is the IQ performance penalty from using file systems in Linux kernel version 2.6 and above?

    Here?s what it boils down to for me?.

    When you use a filesystem how much control do you have over every aspect of the filesystem, block sizes, continuous or striping methods, SAN communication, SAN/NAS block and stripe sizes, etc???

    The worst answer is, I have no control over any of it.  Best case, you can control some or most of it.

    With raw devices, you have complete control.  Or rather, IQ has complete control over everything outside of how the SAN storage is carved up.

    I had one customer that used filesystems for IQ.  Those nice, big fat IOs that IQ likes to do were cut down to 2k for everything.  Which was then sent back to a SAN that like to do nice big IOs, too.  Another customer had a filesystem that used IOs that were slightly larger than what IQ could use and larger than the SAN block size definition.  It caused 2 IOs for every IO that IQ did because the filesystem write was bigger than a single block on the storage, so it had to be broken into 2 physical IOs.

    Lastly, IQ will now want to open all filesystem devices with O_DIRECT.  So you have to make sure you filesystem supports that as well.  If not, then you leave yourself exposed for a situation where IO could be buffered but not on disk yet.

    There is some merit to using journaling as it can help protect your filesystem.  With IQ, though, it will slow it down.  So you have a choice of performance or filesystem protection.

    In the end, it comes down to ease or performance.  Do you want to easily implement IQ or have complete control over how IQ is implemented so that you can control performance?  There is no right or wrong here.  SAP has chosen that IQ will be implemented on filesystems when it is deployed as part of HANA in dynamic tiering.  That was done because HANA is on filesystem and it is easier to continue that with IQ/DT, though it can be changed if you know enough about HANA and DT to do so.  We made the choice to give up some on performance, for now, so that we could have an easier system to deploy.

    I will say, though, that you had become very good friends with the system and storage administrators.  Chances are something will have to be changed so better to be trusted by them up front so changing something is easier.

    Side note??. I would recommend against using the old Sybase.com man pages.  I know they are much easier to traverse, but they are quite old and not maintained.  This section still holds true, but other items have changed in the newer manuals.

    Mark

    Mark Mumy
    Strategic Technology Incubation Group
    SAP Global Center of Excellence |  SAP
    M +1 347-820-2136 | E mark.mumy at sap.com<mailto:mark.mumy at sap.com>
    My Blogs: https://blogs.sap.com/author/markmumy/

    https://sap.na.pgiconnect.com/I825063
    Conference tel: 18663127353,,8035340905#

    From: "iqug-bounces at iqug.org<mailto:iqug-bounces at iqug.org>" <iqug-bounces at iqug.org<mailto:iqug-bounces at iqug.org>> on behalf of Ron Watkins <rwatkins at dssolutions.com<mailto:rwatkins at dssolutions.com>>
    Date: Thursday, July 5, 2018 at 8:08 AM
    To: Chris Baker <c.baker at sap.com<mailto:c.baker at sap.com>>, 'Steve Shen' <sshen at sscinc.com<mailto:sshen at sscinc.com>>, "iqug at iqug.org<mailto:iqug at iqug.org>" <iqug at iqug.org<mailto:iqug at iqug.org>>
    Subject: Re: [IQUG] What is the IQ performance penalty from using file systems in Linux kernel version 2.6 and above?

    Journaling is optional and can  be disabled using the following option to mkfs:
    -O ^has_journal
    The other comments I agree with, and always prefer RAW to FS.
    Ron

    From: Baker, Chris [mailto:c.baker at sap.com]
    Sent: Wednesday, July 04, 2018 1:36 PM
    To: Ron Watkins; 'Steve Shen'; iqug at iqug.org<mailto:iqug at iqug.org>
    Subject: RE: [IQUG] What is the IQ performance penalty from using file systems in Linux kernel version 2.6 and above?

    To add to Ron?s comments ?

    Direct I/O and write-cache bypassing are good starts, but the filesystem choice WILL affect you as well, even as far as IQ page sizes vs. filesystem page sizes (IQ I/O is broken into smaller pieces).  The Linux I/O elevator can play here as well (anticipatory vs. cfq vs. deadline vs. noop) when defining I/O strategies, even for filesystem.

    How the block device (holding the filesystem) is defined can also affect I/O.  Some SANs allow the blocks to be laid out consecutively, so even if the filesystem pages are smaller that IQ pages, the SAN can ?hold? the write for > 1 page, allowing better performance on the read/write as there is a better chance that consecutive blocks will be part of the same logical page.

    I won?t even mention mirroring and the overhead that may cause.

    Of course it goes without saying that you should not share the IQ filesystem for other purposes, in any case.

    EXT4 is also a journaling filesystem.  It will log every,    single,    access ? and can slow down IO drastically.  You can turn off the EXT4 journaling aspects with various mount options and settings, effectively turning it into EXT3, and this can help performance.

    In the end, you probably want to test RAW vs. Filesystem performance yourself to ensure it is within your own SLAs, performance criteria and I.T. specs.  Don?t overlook what I.T. ?thinks? you need or is only willing to provide, with what you MUST provide for your own SLAs to your end users/customers.

    Chris

    Chris Baker | Database Engineering Evangelist | CERT | PI HANA Platform Data Management | SAP T +1 416-226-7033<tel:+1%20416-226-7033> | M +1 647-224-2033<tel:+1%20647-224-2033> | TF +1 866-716-8860<tel:+1%20866-716-8860>
    SAP Canada Inc. 445 Wes Graham Way, Waterloo, N2L 6R2<x-apple-data-detectors://17/1>
    c.baker at sap.com<mailto:c.baker at sap.com> | www.sap.com<http://www.sap.com/>

    https://sap.na.pgiconnect.com/I826572
    Conference tel: 1-866-312-7353,,9648565377#<tel:1-866-312-7353,,9648565377%23>

    From: iqug-bounces at iqug.org<mailto:iqug-bounces at iqug.org> [mailto:iqug-bounces at iqug.org] On Behalf Of Ron Watkins
    Sent: Wednesday, July 4, 2018 4:02 PM
    To: 'Steve Shen' <sshen at sscinc.com<mailto:sshen at sscinc.com>>; iqug at iqug.org<mailto:iqug at iqug.org>
    Subject: Re: [IQUG] What is the IQ performance penalty from using file systems in Linux kernel version 2.6 and above?

    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> [mailto:iqug-bounces at iqug.org] On Behalf Of Steve Shen
    Sent: Wednesday, July 04, 2018 12:15 PM
    To: iqug at iqug.org<mailto: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/doc/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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------------------------------

Message: 2
Date: Thu, 5 Jul 2018 16:40:27 +0000
From: Steve Shen <sshen at sscinc.com>
To: "'Mumy, Mark'" <mark.mumy at sap.com>, "iqug at iqug.org"
        <iqug at iqug.org>
Subject: Re: [IQUG] IQUG Digest, Vol 67, Issue 5
Message-ID:
        <0C03FF7E7FA66E41A61525750FD653399DC5397C at ykt1emxprd6.globeop.com>
Content-Type: text/plain; charset="utf-8"

Hi Mark,

I should not go back to Sybase web-sites anymore.  I will go to SAP web-site from now on.

Thank you for your reminder.

Regards,

Steve

-----Original Message-----
From: Mumy, Mark [mailto:mark.mumy at sap.com]
Sent: Thursday, July 05, 2018 12:26 PM
To: Steve Shen; iqug at iqug.org
Subject: Re: [IQUG] IQUG Digest, Vol 67, Issue 5

Just saw your questions on RHEL versions.

See my other email....  Using the manuals from Sybase.com isn't advised as they are not kept up.  For platform specific stuff and OS certifications, you can only get the currently supported platforms from sap.com, here.  What we list in the manuals was the initial versions supported.  We don't update the manuals when we test newer OS versions, we always update the SAP PAM (product availability matrix).
https://apps.support.sap.com/sap(bD1lbiZjPTAwMQ==)/support/pam/pam.html?smpsrv=https%3a%2f%2fwebsmp106.sap-ag.de#ts=0

See the IQ 16 manual you point to is grossly out of date and only shows RHEL 5 and 6 as supported when the products were first released.  Use the above link and you will see that other versions are included as well.  That link also includes other platform related details that are important for IQ deployment on various platforms.  Here's the link to all Linux versions supported for IQ 16.0:
https://apps.support.sap.com/sap/support/pam?hash=s%3D%26filter%3Dfavorites%257CT%26o%3Dmost_viewed%257Cdesc%26st%3Dl%26rpp%3D20%26page%3D1%26pvnr%3D67838200100900005877%26pt%3Dt%257COS%26fclfilter%3DG1%257CLINUX%2520ON%2520X86_64%26ainstnr%3D67838200104900016656

Our support for OS versions is a tad relaxed.  If it says RHEL 6.2, that doesn?t mean it?s the only version we support.  That's the minimum version we support for the main release of RHEL 6.  Our policy is to support any of the dot releases at that or a higher level.  So not RHEL 6.2, but really RHEL 6.2+ or RHEL 6.x with a minimum of 6.2.  However you want to read it.

With IQ 15.4, you can use whatever OS you want without fear of violating support.  OK, it's not quite THAT easy.  IQ 15.4 is no longer supported.  So any OS that you want to support would be just fine.

Do you have an SAP S-number?  The SAP sites contain quite a lot of details on IQ deployments in the PAM, roadmaps, SAP Notes, and manuals.

Mark

Mark Mumy
Strategic Technology Incubation Group
SAP Global Center of Excellence |  SAP
M +1 347-820-2136 | E mark.mumy at sap.com
My Blogs: https://blogs.sap.com/author/markmumy/

https://sap.na.pgiconnect.com/I825063
Conference tel: 18663127353,,8035340905#

?On 7/5/18, 11:03 AM, "iqug-bounces at iqug.org on behalf of Steve Shen" <iqug-bounces at iqug.org on behalf of sshen at sscinc.com> wrote:

    Today's Topics:

    1. Re: What is the IQ performance penalty from using file
          systems in Linux kernel version 2.6 and above? (Steve Shen)

    2. Re: RedHat Enterprise Linux versions for IQ versions 15.4 and 16.0 (Steve Shen)

    The following are for IQ 15.4 and 16.0 at Linux from the document link http://infocenter.sybase.com/help/topic/com.sybase.infocenter.dc10083.1540/doc/pdf/iqicglin.pdf and http://infocenter.sybase.com/help/topic/com.sybase.infocenter.dc10083.1600/doc/pdf/iqicglin.pdf

    "
    Supported Server Platforms
    Sybase IQ is compatible with these platforms and operating systems.
    * Red Hat Enterprise Linux 6.2 (Linux on POWER; 64-bit)
    * Red Hat Enterprise Linux 6.2 x86-64, Advanced Server and Workstation Editions
    * Red Hat Enterprise Linux 6.0 (Linux onPOWER;64-bit) - minimum patch level Update-2
    * Red Hat Enterprise Linux 6.0 x86-64, Advanced Server and Workstation Editions -
    minimum patch level Update-2
    * Red Hat Enterprise Linux 5.5 (Linux onPOWER;64-bit) - minimum patch level Update-2
    * Red Hat Enterprise Linux 5.5 x86-64, Advanced Server and Workstation Editions -
    minimum patch level Update-2
    * SuSE Linux Enterprise Server (SLES) 11.0 x86-64 - minimum patch level SP1
    * SuSE Linux Enterprise Server (SLES) 11.0 (Linux on POWER; 64-bit) - minimum patch
    level SP1
    Supported Client
    "
    Red Hat Enterprise Linux 5.5 x86-64 or 6.0 x86-64 or 6.2 x86-64 are very old.

    Can I used Red Hat Enterprise Linux version 6.8 or 7.4?  Please advise.  Thank you.

    Regards,

    Steve

    -----Original Message-----
    From: iqug-bounces at iqug.org [mailto:iqug-bounces at iqug.org] On Behalf Of iqug-request at iqug.org
    Sent: Thursday, July 05, 2018 11:42 AM
    To: iqug at iqug.org
    Subject: IQUG Digest, Vol 67, Issue 5

    Send IQUG mailing list submissions to
            iqug at iqug.org

    To subscribe or unsubscribe via the World Wide Web, visit
            http://iqug.org/mailman/listinfo/iqug
    or, via email, send a message with subject or body 'help' to
            iqug-request at iqug.org

    You can reach the person managing the list at
            iqug-owner at iqug.org

    When replying, please edit your Subject line so it is more specific than "Re: Contents of IQUG digest..."


    Today's Topics:

       1. Re: What is the IQ performance penalty from using file
          systems in Linux kernel version 2.6 and above? (Steve Shen)


    ----------------------------------------------------------------------

    Message: 1
    Date: Thu, 5 Jul 2018 15:41:43 +0000
    From: Steve Shen <sshen at sscinc.com>
    To: "'Mumy, Mark'" <mark.mumy at sap.com>, Ron Watkins
            <rwatkins at dssolutions.com>, "Baker, Chris" <c.baker at sap.com>,
            "iqug at iqug.org" <iqug at iqug.org>
    Subject: Re: [IQUG] What is the IQ performance penalty from using file
            systems in Linux kernel version 2.6 and above?
    Message-ID:
            <0C03FF7E7FA66E41A61525750FD653399DC52633 at ykt1emxprd6.globeop.com>
    Content-Type: text/plain; charset="utf-8"

    Hi Mark,

    The senior management had chosen ?ease? over ?performance?.

    Thank you very much for your feedback.

    Regards,
    Steve
    From: Mumy, Mark [mailto:mark.mumy at sap.com]
    Sent: Thursday, July 05, 2018 11:10 AM
    To: Ron Watkins; Baker, Chris; Steve Shen; iqug at iqug.org
    Subject: Re: [IQUG] What is the IQ performance penalty from using file systems in Linux kernel version 2.6 and above?

    Here?s what it boils down to for me?.

    When you use a filesystem how much control do you have over every aspect of the filesystem, block sizes, continuous or striping methods, SAN communication, SAN/NAS block and stripe sizes, etc???

    The worst answer is, I have no control over any of it.  Best case, you can control some or most of it.

    With raw devices, you have complete control.  Or rather, IQ has complete control over everything outside of how the SAN storage is carved up.

    I had one customer that used filesystems for IQ.  Those nice, big fat IOs that IQ likes to do were cut down to 2k for everything.  Which was then sent back to a SAN that like to do nice big IOs, too.  Another customer had a filesystem that used IOs that were slightly larger than what IQ could use and larger than the SAN block size definition.  It caused 2 IOs for every IO that IQ did because the filesystem write was bigger than a single block on the storage, so it had to be broken into 2 physical IOs.

    Lastly, IQ will now want to open all filesystem devices with O_DIRECT.  So you have to make sure you filesystem supports that as well.  If not, then you leave yourself exposed for a situation where IO could be buffered but not on disk yet.

    There is some merit to using journaling as it can help protect your filesystem.  With IQ, though, it will slow it down.  So you have a choice of performance or filesystem protection.

    In the end, it comes down to ease or performance.  Do you want to easily implement IQ or have complete control over how IQ is implemented so that you can control performance?  There is no right or wrong here.  SAP has chosen that IQ will be implemented on filesystems when it is deployed as part of HANA in dynamic tiering.  That was done because HANA is on filesystem and it is easier to continue that with IQ/DT, though it can be changed if you know enough about HANA and DT to do so.  We made the choice to give up some on performance, for now, so that we could have an easier system to deploy.

    I will say, though, that you had become very good friends with the system and storage administrators.  Chances are something will have to be changed so better to be trusted by them up front so changing something is easier.

    Side note??. I would recommend against using the old Sybase.com man pages.  I know they are much easier to traverse, but they are quite old and not maintained.  This section still holds true, but other items have changed in the newer manuals.

    Mark

    Mark Mumy
    Strategic Technology Incubation Group
    SAP Global Center of Excellence |  SAP
    M +1 347-820-2136 | E mark.mumy at sap.com<mailto:mark.mumy at sap.com>
    My Blogs: https://blogs.sap.com/author/markmumy/

    https://sap.na.pgiconnect.com/I825063
    Conference tel: 18663127353,,8035340905#

    From: "iqug-bounces at iqug.org<mailto:iqug-bounces at iqug.org>" <iqug-bounces at iqug.org<mailto:iqug-bounces at iqug.org>> on behalf of Ron Watkins <rwatkins at dssolutions.com<mailto:rwatkins at dssolutions.com>>
    Date: Thursday, July 5, 2018 at 8:08 AM
    To: Chris Baker <c.baker at sap.com<mailto:c.baker at sap.com>>, 'Steve Shen' <sshen at sscinc.com<mailto:sshen at sscinc.com>>, "iqug at iqug.org<mailto:iqug at iqug.org>" <iqug at iqug.org<mailto:iqug at iqug.org>>
    Subject: Re: [IQUG] What is the IQ performance penalty from using file systems in Linux kernel version 2.6 and above?

    Journaling is optional and can  be disabled using the following option to mkfs:
    -O ^has_journal
    The other comments I agree with, and always prefer RAW to FS.
    Ron

    From: Baker, Chris [mailto:c.baker at sap.com]
    Sent: Wednesday, July 04, 2018 1:36 PM
    To: Ron Watkins; 'Steve Shen'; iqug at iqug.org<mailto:iqug at iqug.org>
    Subject: RE: [IQUG] What is the IQ performance penalty from using file systems in Linux kernel version 2.6 and above?

    To add to Ron?s comments ?

    Direct I/O and write-cache bypassing are good starts, but the filesystem choice WILL affect you as well, even as far as IQ page sizes vs. filesystem page sizes (IQ I/O is broken into smaller pieces).  The Linux I/O elevator can play here as well (anticipatory vs. cfq vs. deadline vs. noop) when defining I/O strategies, even for filesystem.

    How the block device (holding the filesystem) is defined can also affect I/O.  Some SANs allow the blocks to be laid out consecutively, so even if the filesystem pages are smaller that IQ pages, the SAN can ?hold? the write for > 1 page, allowing better performance on the read/write as there is a better chance that consecutive blocks will be part of the same logical page.

    I won?t even mention mirroring and the overhead that may cause.

    Of course it goes without saying that you should not share the IQ filesystem for other purposes, in any case.

    EXT4 is also a journaling filesystem.  It will log every,    single,    access ? and can slow down IO drastically.  You can turn off the EXT4 journaling aspects with various mount options and settings, effectively turning it into EXT3, and this can help performance.

    In the end, you probably want to test RAW vs. Filesystem performance yourself to ensure it is within your own SLAs, performance criteria and I.T. specs.  Don?t overlook what I.T. ?thinks? you need or is only willing to provide, with what you MUST provide for your own SLAs to your end users/customers.

    Chris

    Chris Baker | Database Engineering Evangelist | CERT | PI HANA Platform Data Management | SAP T +1 416-226-7033<tel:+1%20416-226-7033> | M +1 647-224-2033<tel:+1%20647-224-2033> | TF +1 866-716-8860<tel:+1%20866-716-8860>
    SAP Canada Inc. 445 Wes Graham Way, Waterloo, N2L 6R2<x-apple-data-detectors://17/1>
    c.baker at sap.com<mailto:c.baker at sap.com> | www.sap.com<http://www.sap.com/>

    https://sap.na.pgiconnect.com/I826572
    Conference tel: 1-866-312-7353,,9648565377#<tel:1-866-312-7353,,9648565377%23>

    From: iqug-bounces at iqug.org<mailto:iqug-bounces at iqug.org> [mailto:iqug-bounces at iqug.org] On Behalf Of Ron Watkins
    Sent: Wednesday, July 4, 2018 4:02 PM
    To: 'Steve Shen' <sshen at sscinc.com<mailto:sshen at sscinc.com>>; iqug at iqug.org<mailto:iqug at iqug.org>
    Subject: Re: [IQUG] What is the IQ performance penalty from using file systems in Linux kernel version 2.6 and above?

    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> [mailto:iqug-bounces at iqug.org] On Behalf Of Steve Shen
    Sent: Wednesday, July 04, 2018 12:15 PM
    To: iqug at iqug.org<mailto: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/doc/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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