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Gatekeepers - All You Need to Know

rticle Number:000074113 Version:2ey Information

udience: Level 30 = Customers Article Type: Break Fix

ast Published: Mon Oct 28 05:05:06 GMT 2013 Validation Status: Final Approved

mmary:

Article Content

mpact:Gatekeepers - All You Need to Know

Gatekeepers or Gate Keepers (GTK or GK) explained.

How do I configure Gatekeepers?

Frequently Asked Questions (FAQ):

What are the most important things to know about Gatekeepers?What is a Gatekeeper?Do I really need to use Gatekeepers?Do I need to create Gatekeepers?Why does the Symmetrix use Gatekeepers and not some other means of control?

Are there devices that should be used as Gatekeepers? Can thin devices be used?notHow many Gatekeepers do I need?

How big should Gatekeepers be?Can I share Gatekeepers across servers?Can I share server resources like HBAs between production applications and Gatekeepers?Does the number of needed Gatekeepers change for different software releases?How do Open Systems and Mainframe Gatekeepers differ?Besides creating Gatekeepers, are there other things I need to set up to use them correctly?Can I use PowerPath with Gatekeepers and is there a reason to do so?Can I use other multi-pathing products with Gatekeepers?Virtualization, Cluster, Migration, or Application Specific Gatekeeper Requirements (Clusters, VirtualServers, Migrations)Can I configure GateKeeper's on Unisys Mainframe host ports? Refer to 84279What are the Gatekeeper requirements for RecoverPoint and Splitter appliance with the Symmetrix Sy

sue:A Gatekeeper cannot be opened because it (or they) are either locked or inaccessible.

nvironment: Product: SymmetrixProduct: Symmetrix VMAX Series

esolution:1. What are the most important things to know about Gatekeepers?

If the system selects and uses a data or system device as a Gatekeeper, applications on the

application host can be impacted! EMC STRONGLY recommends that dedicated Gatekeepe

See below.created and used. This is particularly important with Open Systems operation.


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Gatekeeper operation for Open Systems and Mainframe operation is similar in principle but there amajor differences. Read below for more information about Open Systems operation and refer to EMKnowledgebase solution for more information about Mainframe Gatekeeper operation.51197

PowerPath be used with Gatekeepers and there is a great reason to do so (refer to item 15canbelow). No other multi-pathing products can be used to define multiple paths to those Gatekeeperdevices.

2. What is a Gatekeeper?

Solutions Enabler and Mainframe Enabler are EMC software components used to control thefeatures of Symmetrix arrays. They receive user requests from CLI, GUI, or other means, andgenerate low-level commands (syscalls) that are transmitted into the Symmetrix array for action.

Gatekeeper devices are Symmetrix devices that act as the target of command requests toEnginuity based functionality. These commands arrive in the form of disk I/O requests (and so a"disk" must be named by the host as the "address" or target of that command). The morecommands that are issued from the host, and the more complex the actions required by thosecommands are, the more gatekeepers and/or array processor resources that are required to handlethose requests in a timely manner.

3. Do I really need to use Gatekeepers?

If Symmetrix commands are running successfully requesting a Symmetrix command, it meansthat a device is being used as a Gatekeeper; the command has to be sent to something the HostBus Adaptor can address, that is, a device. The larger question is what is the nature of thatGatekeeper? Is it a user device used to hold data or is it a system paging disk? If so, there is aserious risk of application impact. This is why EMC strongly recommends the use of dedicatedGatekeepers, as described below.

4. Do I need to create Gatekeepers?

Open Systems:

Open Systems servers should use dedicated Symmetrix devices (that is, dedicated to being aGatekeeper with no other purpose) for Gatekeeper purposes. Solutions Enabler selectsa Gatekeeper device for a given command based upon a hierarchy of choices (found in SolutionsEnabler documentation) and could be forced to utilize a device that is used by a database or by theoperating system if not enough dedicated Gatekeepers are defined. If this happens, it cansignificantly impact applications that may be operating on a server.

A Gatekeeper device may not respond to an application or server I/O request until a Symmetrixcommand request is completed. If a Symmetrix is executing a complex or time-consuming

command, such as a query of the Remote R2 Symmetrix, line latency may cause a delay and thedevice can, in effect, be locked for some time. If the time is too long, the application using thatGatekeeper as a data device may experience I/O timeouts or perform poorly.

Mainframe:

Mainframe generally requires users to name a device that is used as a target of a syscall. Somemainframe commands and applications can select devices from a pool. Refer to EMCKnowledgebase solution for more information. The mainframe information in51197this Knowledgebase solution is only to illustrate differences between mainframe and opensystems and is not complete.


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Gatekeepers should be created if there are no existing devices already dedicated to Gatekeeperuse. Refer to EMC Knowledgebase solution for "How to use Solutions Enabler to create15432Mainframe Gatekeeper devices".

5. Why does the Symmetrix use Gatekeepers and not some other means of control?

The Symmetrix is a high performance storage system that scales up to the largest storagecapacities available in the industry. It also has very comprehensive monitoring, performance and

diagnostic capabilities. As a result, command dialogs with the system can be extensive and caninvolve a good deal of data. Symmetrix uses Gatekeepers as a scalable, high-performance meansof command and control, suitable to the capabilities of the array. The deterministic nature of disk I/O is particularly powerful when used for array-wide or multi-array operations such as consistentsplits, in which conventional networking may encounter packet collisions or retries, which couldprevent the timely operation of disaster recovery commands.

6. Are there devices that should NOT be used as Gatekeepers? Can thin devices be used?

Open Systems:

There are devices that should not be used as Gatekeepers. The rule of thumb is,"do not usedevices that have user or system data on them" to avoid conflict and I/O performance issues whenoperating Symmetrix features. This is why EMC makes the strong recommendation to dedicatedevices exclusively for Gatekeeper use. There are three means to explicitly control what deviceswill or will not be used as Gatekeepers:

Devices that absolutely should not be used as Gatekeepers can be put into a gkavoid file aspart of the Solutions Enabler setup. This prevents devices in that file from being used asGatekeepers, yet still permits Solutions Enabler the freedom to select other devices asGatekeepers as required. Note that adding new devices to a server or application mayrequire updating this file with those devices. Refer to EMC Knowledgebase solution 4160

for Setting up gkavoid files.Devices intended for Gatekeeper use only can be put into the gkselect file. Devices in thisfile will take priority in the selection process. Solutions Enabler may choose data devices asa Gatekeeper for a particular Symmetrix if none its Gatekeepers in the gkselect file exist, orare offline.After determining how many gatekeepers are needed, create dedicated Gatekeepers, and setthe storapid daemon option, gk_use in the daemon_options file to specify dedicated only.(storapid:gk_use=dedicated_only)Meta Devices cannot be configured as Gatekeepers.Thin devices, aka Virtual Devices used with EMC Virtual Provisioning, CAN be used asgatekeepers. All the existing gatekeeper rules apply, and the thin gatekeeper device doesnot need to be bound to any storage pool.

7. How many Gatekeepers do I need?

Open Systems:

The answer is, "Enough to perform all concurrent Symmetrix commands and queries withoutrunning into a condition in which commands are delayed or rejected for lack of a gatekeeperresource." Practically speaking, any server issuing commands to a Symmetrix, physical orvirtual, should have six Gatekeeper devices uniquely available to it. Details of their creation andcharacteristics are found elsewhere in this Knowledgebase solution.


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Six Gatekeepers should prove sufficient for any Open Systems control server (meaning a serverthat is sending control syscalls to the Symmetrix instead of, or in addition to, data), except thoserunning Consistency Groups (more in the paragraph below). More than six can be needed undervery heavy management workloads, such as heavy use of ControlCenter Performance Managerand/or Symmetrix Performance Manager, or for certain other circumstances (refer to item 16below).

For those locations utilizing Consistency Groups, add the following device count to the six

devices mentioned above. Here is how to calculate the required Gatekeeper count:

Solutions Enabler 7.0:In addition to the six above, another fourteen Gatekeepers must be added if thereis performance-critical SRDF operation, plus for [Number of CGs] * 0.5 = Gatekeepersneeded for Consistency Group operation.Solutions Enabler 7.1:[Number of CGs] * 0.5 = Gatekeepers needed for Consistency Group operationSolutions Enabler 7.2:[Number of CGs] * 0.3 = Gatekeepers needed for Consistency Group operation

Round up the result of calculations in bullets 2 and 3 above to whole integers and then do thefollowing addition:6 + (those needed for 7.0 with SRDF) + (GKs needed for CG operation) = total number of Gatekeepers to specify.

8. How big should Gatekeepers be?

Gatekeepers require only a small amount of space, 3 MB (3 cyl) for Enginuity levels 57xx, 58xx

and higher, and 3 MB (6 cyl) for Enginuity levels of 56xx and lower. Users are encouraged to notbuild Gatekeepers in larger sizes as the small size is used by Enginuity to automatically identifyand use devices as Gatekeepers. Devices under 8 MB have the indication GK in syminq

output. Gatekeeper devices must be mapped and masked to single servers only and should benot

shared across servers. For Virtual Server and Cluster environments, refer to the importantadditional information in item 16 below.

Gatekeepers should be RAID protected in some way so if the device were to fail, the syscallwould be directed to the "mirror" of the failed device. Any RAID format will provide thisprotection, but a simple mirror (RAID 1) is suggested. Other RAID configurations take a bitmore space, for example, to make it 7+1 involves spreading the gatekeeper across 8 drives (noactual I/O goes to the disk, so there is no 'I/O' penalty). In such a case, your 3 cyl gatekeeper willtake (7+1)*3= 24 cylinders. A nit, but for completeness' sake...

9. Can I share Gatekeepers across servers?

Gatekeeper devices must be mapped and masked to single hosts and should be sharedonly notfor concurrent I/O across hosts. For Virtual Server and Cluster environments, refer to theimportant additional information in item 16 below. See the note about Multi-pathed Gatekeepersupport with Symmetrix Enginuity 5876.

10. Can I share server resources like HBAs between production applications and Gatekeepers?


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Many configurations have Solutions Enabler and control commands running from a productioncontrol server. Just as production applications have requirements for minimal response times,certain Symmetrix management and control operations should be deemed real time and critical(consistency protection is a good example).

While gatekeepers can share HBAs and FA ports with production hosts, there are good reasons toisolate them to separate HBAs and FA ports.

Perhaps most critical, consistency related commands needed for proper disaster protectionmay be held up by pending I/O's previously issued by a shared HBA (some HBAs will stopsending until some of the pending I/Os finish).Applications on that HBA could be impacted by syscall traffic. An overworked server canalso cause Symmetrix control issues, because the server itself can be too busy to send atime-critical control operation to the Symmetrix.

It is always a best practice to isolate Gatekeepers on production servers to HBA and FA ports thatare not response time sensitive and are not busy with production I/O. It is possible for gatekeepersto share FA ports as long as a given Gatekeeper is used only by a given control server.

11. Does the number of needed Gatekeepers change for different software releases?

Open Systems:

The minimum number of Gatekeepers needed does change over time as EMC works to makecontrol software more efficient. The numbers provided in this Knowledgebase solution can beused with available releases.

12. How do Open Systems and Mainframe Gatekeepers differ?

While the underlying principles involved are identical, the differing nature of Mainframe I/O and

SCSI I/O results in behaviors that are not identical. Refer to EMC Knowledgebase solution 51197for Mainframe Gatekeeper information. This Knowledgebase solution is written with a focus onOpen Systems and contains only partial Mainframe information.

13. Besides creating Gatekeepers, are there other things I need to set up to use them correctly?

Yes. Make them a suitable size (see above). Be sure they are not SRDF, or virtualor snap devices, or devices in a save pool or thin pool.

14. Can I use PowerPath with Gatekeepers and is there a reason to do so?

Yes, and there is good reason to do so. Many Open Systems customers double the Gatekeepercount, with half on each of two paths. With this configuration, in the event of path failure, theSymmetrix could still receive commands. PowerPath protects against path failure without theneed to double the device count.

15. Can I use other multi-pathing products with Gatekeepers?

No. Other multi-pathing products may be used to define multiple paths with Gatekeepers.notPowerPath uniquely recognizes Symmetrix commands and treats them in a special manner whenmultiple paths are available to the Gatekeeper device. Products without this awareness can, forexample, retry the I/O and cause significant issues with the command processing.


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16. Virtualization/Cluster/Migration or Application Specific Gatekeeper Requirements.

Virtual Server EnvironmentsVirtual Server environments often permit the movement of a guest operating system instance from physical server to another. If that instance is doing Symmetrix management or control, the Gatekeebeing used must be visible to that instance on whatever physical server it is running upon. As a resuthe Gatekeeper devices must be made visible to the various physical servers the guest may operate

upon. Note that the rule for sharing Gatekeepers remains, and that the guest operating system inotwith its Solutions Enabler instance must run on only one physical machine at any given time, and oone instance using the Gatekeeper at any one time. Please also see EMC Knowledgebase solution 7.

Clustered EnvironmentsClustered environments also involve the movement of Symmetrix management and control from onserver to another as part of a failover process. There are different types of clusters and the reader shlook at the ELab Host Connectivity Guide of the particular operating system for details of their clusconfiguration. With shared nothing clusters, the Gatekeepers should be visible to all the physical sethat may issue commands to the Symmetrix, in order to continue operations after a failover from thcontrolling node. And as above, commands to a given Gatekeeper must be issued by only one conserver instance at a time. In a share everything cluster (OpenVMS for example), a Gatekeeper must

mapped and masked to only one, and only one, server, in order to restrict Gatekeeper usage to the ocontrolling server.

SRDF/CEEach Symmetrix must be configured with the recommended number of gatekeepers per node, per Sside for SRDF/CE exclusive use, and must be configured per the above information. They should ahave Windows disk signatures so that they are fully visible to the cluster. For performance reasonsrecommended that an additional gatekeeper be associated with every SRDF/CE device group.

PowerPath Migration Enabler (PPME)

Gatekeeper devices should be migrated. Gatekeepers should not be migrated by any means becnotthe new location will have a different context than the old location, and commands issued tothe migrated Gatekeeper could result in unintended consequences in the new array.

ControlCenter Agent and Symmetrix Management Console (SMC)Both be serviced by the recommended Gatekeeper count above. Note that large specific workloads,as often collecting performance data for Symmetrix Performance Analyzer orPerformance Manager, could require more Gatekeepers for proper operation.

Refer to17. Can I configure GateKeeper's on Unisys Mainframe host ports? 84279

18. What are the Gatekeeper requirements for RecoverPoint and Splitter appliance with the Symm

System?

Starting with RecoverPoint 3.5 and Enginuity 5876, tagging all VMAX devices exposed toRecoverPoint (including production and replica volumes, journal volumes, the repository, andgatekeepers) is required. Untagged volumes will not be available in RecoverPoint for host-based,fabric-based, and Symmetrix splitters. RecoverPoint manages the Symmetrix splitter using Solutions Enabler. Solutions Enabler commanare sent to the Symmetrix array via gatekeepers. Gatekeepers are small, 3-cylinder devices(approximately 3 MB) that are used to send control commands to the Symmetrix. RecoverPoint site control manages the resources of the RecoverPoint cluster, including the Symmesplitter. The active instance of RecoverPoint cluster site control can run only on either RPA1 or RPeven if there are more RPAs in the cluster. As a result, the gatekeepers must be presented to RPA1


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RPA2 only.

RPA1 must have access to eight gatekeepers; RPA2 must have access to eight different gatekeepersgatekeeper should not be shared with any other RPA or host. RPAs must have access to theirgatekeepers via multiple redundant paths. If a site comprises multiple Symmetrix splitters or multipRecoverPoint clusters, a total of 16 gatekeepers is required for eachSymmetrix-splitter/RecoverPoint-cluster combination.

Host-based Access Control is an optional feature used by a Symmetrix administrator to set up andrestrict host access to defined sets of devices (access pools). If Access Control is used, RecoverPoiappliances must be granted access to their devices (gatekeepers, repository, journals, and productioreplica volumes). To accommodate RecoverPoint, a new access right, RPA, has been added. For minformation, refer to EMC Solutions Enabler Symmetrix Array Management Product Guide, sectioHost-based access control. Journal volumes, repository, and gatekeepers may use dedicated FA ports. Add these FA ports intosame RPA-to-Symmetrix zones.

For Symmetrix splitter only, expose gatekeepers (3-cylinder devices), 16 per RecoverPoint cluster:

Create a port group for RPA1 gatekeepers or use an existing port group. For optimal performuse 8 FA ports.Create RPA1 gatekeeper storage group with 8 gatekeepers designated for RPA1.Create a masking view with the RPA1 gatekeeper port group, RPA1 gatekeeper storage grouand RPA1 initiator group.Create a port group for RPA2 gatekeepers or use an existing port group. For optimal performuse 8 different FA ports from those used for the RPA1 gatekeepers.Create RPA2 gatekeeper storage group and add 8 different gatekeepers from the ones exposeRPA1.Create a masking view with the RPA2 gatekeeper port group, RPA2 gatekeeper storage grouand RPA2 initiator group.

If the host storage group contains any gatekeepers, RecoverPoint will incorrectly assume that thesethe dedicated gatekeepers it can use with the Symmetrix splitter. Therefore, host gatekeepers shoulseparated into a different host storage group, not accessible by RPA's. To display the Symmetrix gatekeepers, use the RecoverPoint CLI command

.show_symmetrix_gate_keepers

Refer to EMC RecoverPoint Deploying with Symmetrix Arrays and Splitter Technical Notes for additioninformation.

otes:Update - May 2012 - New for Solutions Enabler 7.4 and Enginuity 5876.

Thin devices are now supported as gatekeeper candidates.The gatekeeper selection algorithim now ignores the fact that a device happens to be a thin device whenslecting gatekeeper candidates. This makes all thin devices candidates for Gatekeeper Selection so we strecommed using dedicated Gatekeeper devices. The thin Gatekeeper device does not have to be bound topool.The following restrictions apply:

Hyper-V thin devices must be bound to a poolNO AS400 Support for using thin devices as Gatekeepers.


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Rules for Multi-Pathing GateKeepersUntil now, we have only supported multipathed Gatekeepers when running EMC Powerpath. BeginningEnginuity 5876 and Solutions Enabler 7.4, we will support a limited set of third party multipathing soluton a limited set of platforms. The following Multipathing Software applications is will be supported;Powerpath, Veritas, and Native Multipathing. These are supported, on AIX, HPUX, Linux, Solaris, andWindows.As always, See E-Lab Navigator for an up-to-date list of supported versions of what EMC supports.

If a host does not have dedicated Gatekeepers (devices 10 Cyls or less), Solutions Enabler selectsGatekeepers as described in the install guide. If the selected Gatekeeper is larger than 10 Cyls, multipat(non-Powerpath), and Enginuity is below 5876, unexpected results may occur. With Solutions Enabler 7

and Enginuity 5876, these devices will be rejected as Gatekeeper candidates. Therefore, it is STRONGLrecommended that you map several dedicated Gatekeepers to the host as described in this solution.

The recommeded size for the ACLX device is 10 cylinders or less. This allows the ACLX device to takeadvantage of the multipathed gatekeeper support in Enginuity 5876. If an ACLX device is multipathed ais more than 10 cylinders, it will not benefit from all the multipathing benefits that 5876 provides.

Prior to SE 7.4 and Enginuity 5876, multipathed Gatekeepers without PowerPath may have workeStarting with Solutions Enabler 7.4, Gatekeeper selection has become stricter when running third partymultipathing software. What may have worked before may not work with Solutions Enabler 7.4 andEnginuity versions prior to 5876.

New log files

A new log file is automatically created in the symapi/log directory. The Gatekeeper Selection Reportprovides details about all physical devices mapped to the host. The report will be updated every time adiscover is performed or when the base daemon (AKA Storapid Daemon) detects a change in the topolog

Important NoteIf using thin Gatekeepers with Hyper-V, the Gatekeepers MUST be bound to a pool. You must weigh thpros/cons of using thin Gatekeepers in this environment, vs the traditional way.

Article Metadata

oduct: Symmetrix, TimeFinder, Solutions Enabler, Symmetrix Remote Data Facility (SRDF), Symmetrix VMAX S

xternal Source: Primus

imus/Webtop solution ID: emc255976

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