[IQUG] IQ 16 Multiplex shared disk cluster

Mark Mumy markdmumy at gmail.com
Thu Aug 24 06:54:27 MST 2017


I wrote that part of the note.  You’ve quoted it out of context.  In fact, the note also says "SAP IQ does not require LVM software”.

It was written in the context of a customer that wants to use an LVM to manage IQ storage in a multiplex.  That’s different than saying that IQ requires an LVM.  The requirement is from the LVM side.  LVMs will safeguard their storage.  A standard LVM makes sure that the disks it controls are only able to be used on a single node.  The cluster versions (VxCFS from Veritas, for instance) put in all the node to node communication into the LVM so that each node knows what others are doing, etc.  It allows for each machine to have full read write access to the disks simultaneously.

If you are using raw devices, then there is no need for anything other than the OS and raw devices that are visible on all nodes.  You could use an LVM to manage the disks, but that is an operational decision that is not required for IQ.

If you are wanting to use filesystems, then you can only use NFS, MapR-FS, or GPFS (IBM), though we have customers using Veritas filesystems in a MPX..  Those are the only supported filesystems for multiplex and are only on Linux.

Mark

> On Aug 24, 2017, at 18:55, Baker, Chris <c.baker at sap.com> wrote:
> 
> This is only for if you want to use an LVM.  An LVM is NOT a requirement.  Read the quotes from the HW Sizing Guide. <>
>  
> All the note discusses is that you MAY use an LVM if you like, but there are requirements that if you elect to use an LVM (e.g. due to IT requirements, corporate policies, etc) then IQ may support it, but you MUST set it up the use shared RW for each node, which most likely will increase costs of the deployment due to additional configuration or licensing of the ‘RW’ capabilities.
>  
> The docs also state that raw devices are supported:
> https://help.sap.com/viewer/a8986af484f21015b55bed80129dc962/16.1.2.0/en-US/a242aca184f2101585f4d110845df83a.html <https://help.sap.com/viewer/a8986af484f21015b55bed80129dc962/16.1.2.0/en-US/a242aca184f2101585f4d110845df83a.html>
>  
> One of the best features to come out of IQ MPX recently, however, is the ability to create a ‘shared nothing’ multiplex.  You might want to also look into this.  With this capability, you can actually use OS filesystem files (and even node-only RW LVM without the additional licensing for sharing) because the IQ devices do not need to be shared across nodes (and you don’t have to define a partition scheme to distribute the data across the nodes – a definite bonus vs. traditional MPP systems).
>  
> You might want to look into this, especially if your organization is looking at VM or Cloud deployments.
>  
> 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>
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>  
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>  
> From: Antonian, Vahe [mailto:vahe.antonian.2 at credit-suisse.com <mailto:vahe.antonian.2 at credit-suisse.com>] 
> Sent: Thursday, August 24, 2017 9:11 AM
> To: Baker, Chris <c.baker at sap.com <mailto:c.baker at sap.com>>; iqug at iqug.org <mailto:iqug at iqug.org>
> Subject: RE: IQ 16 Multiplex shared disk cluster
>  
> https://launchpad.support.sap.com/#/notes/2108144 <https://launchpad.support.sap.com/#/notes/2108144>
>  
> In an IQ Multiplex environment, comprised of multiple nodes, the cluster version of a Logical Volume Manager (CLVM) must be used so that each node can access the disks. This will cost more and also add to infrastructure complexity.
>  
> Vahe Antonian 
> Database IB Ops Service 
> +1 212 538 1642 (*106 1642) 
> From: Baker, Chris [mailto:c.baker at sap.com <mailto:c.baker at sap.com>] 
> Sent: Thursday, August 24, 2017 9:06 AM
> To: Antonian, Vahe (MLEA 42); iqug at iqug.org <mailto:iqug at iqug.org>
> Subject: RE: IQ 16 Multiplex shared disk cluster
>  
> You don’t need anything.  Not sure where you are reading about a clustered LVM as a definite requirement (please provide the link).  For some platforms, we do now support some cluster/shared LVM solutions, per the docs, but in reality, IQ MPX was designed to not need anything at all.  This avoids the performance degradations implicit in a shared RW LVM, and the cost. 
>  
> All you really need is RW access to the same raw partitions mounted to each node from a SAN.  IQ manages all the locking internally to prevent concurrent access to the same block by multiple nodes (something that is then redundant with a shared RW LVM, but at an added cost).
>  
> The raw partitions on the SAN are mounted as devices under /dev as block devices, then converted to /dev/raw character devices with ownership of the raw devices changed to be RW only by the invoker of the IQ server.
>  
> I suggest using symlinks in the .db directory to point to the /dev/raw devices to allow ease of portability and also makes creating the multiplex easier, especially in cases where you may have other block or raw devices mounted in different places on different nodes.
>  
> Attached are examples of the rules you need to convert the block devices to character raw devices under RHEL.  IMHO this is much more preferable than using a rawservice as the rules fire before services, allowing you to start IQ as a service (daemon) if you desire.
>  
> HTH
> 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 <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 <mailto:iqug-bounces at iqug.org>] On Behalf Of Antonian, Vahe 
> Sent: Thursday, August 24, 2017 8:12 AM
> To: iqug at iqug.org <mailto:iqug at iqug.org>
> Subject: [IQUG] IQ 16 Multiplex shared disk cluster
>  
> Curious what folks are using as their shared disk cluster software for IQ 16 Multiplex on Redhat (RHEL 6). SAP online whitepapers and knowledgebase articles have little to no detail and simply state that a clustered LVM is needed for the nodes to share the devices.
>  
> Thanks,
>  
> Vahe Antonian
> CREDIT SUISSE
> Information Technology | Database IB Ops Service, MLEA 42
> One Madison Avenue | New York NY 10010 | Americas
> Phone +1 212 538 1642
> vahe.antonian.2 at credit-suisse.com <mailto:vahe.antonian.2 at credit-suisse.com> | www.credit-suisse.com <http://www.credit-suisse.com/>
>  
> 
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