power vault in symmetrix dmx 3 and dmx 4 systems operational overview and best practices technical...

7/27/2019 Power Vault in Symmetrix DMX 3 and DMX 4 Systems Operational Overview and Best Practices Technical Note

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Executive summary

Power Vault in Symmetrix DMX-3 and DMX-4 Systems: Operational Overview and Best Practices

EMC Confidential – Internal use only

Executive summary

A key to Symmetrix® DMX‘s resiliency is its ability to maintain dataintegrity during power outages. Each Symmetrix storage array comes with

battery backup in order to safely power down the array in the event of powerloss. Ensuring that all data tracks in memory are successfully written to diskis essential to maintaining the consistency of application data stored on theSymmetrix.

As cache size, disk size, and power requirements have grown, the timerequired to vault data in the event of a power outage has also increased. PowerVault is designed to limit the time needed to power off the system if it needs toswitch to a battery supply.

Upon detecting the need to come offline or power down, the system stops all

I/O and the DAs start writing the contents of the appropriate areas of globalmemory to special vault devices located on each DA. The vault image is fullyredundant, with the specified contents of global memory being saved twice toindependent disks. When the DAs are done writing (saving) everything tothese vault disks, the machine either finishes powering down or remains at theoffline state if it doesn’t need to power down.

When the machine is powered back up, the DAs write all the saved informationon the Power Vault devices back to all the correct locations in global memory.Write-pending or format-pending tracks that were in cache before the powerdown will be restored to cache.

Introduction

Vault save operations are triggered automatically by environmental conditions.Vaulting can also be initiated by manually powering down a system or takingthe disk directors offline.

When performing a vault operation, the Symmetrix uses disk storage calledPower Vault devices. Power Vault devices are volumes on designated physicaldisk drives that reserve a dedicated 5 GB space each for vaulting data,including metadata, from global memory during a powerdown operation.During powerup, the data is written back to global memory to restore thesystem.

Power Vault devices are configured on the first four disk drives on each drive

loop in the direct-attached storage bay. For each pair of disk directors 160 GB of total capacity is reserved for vault devices.

This technical note describes the vault save and restore operations,configuration options and rules, and environmental monitoring. Best practice



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Power subsystem overview

Power Vault in Symmetrix DMX-3 and DMX-4: Operational Overview and Best Practices


recommendations for powerdown and powerup procedures, as well as forpreventing accidental triggering of a vault save operation, are also included.

AudienceThis internal technical note is intended for technology professionals whosupport Symmetrix systems.

The Power Vault in EMC Symmetrix DMX-3 and Symmetrix DMX-4 Systems white paper contains much of the same information found here without thedetailed commands and tools. This document is available on EMC.com andPowerlink® and is the document customers should reference.


The power subsystem architecture provides two completely separate power

zones (Power Zone A and Power Zone B), each of which can maintain powerfor an entire system bay or storage bay independent of the operation of thesecond zone. There is no redundancy within each zone; rather the redundancyis accomplished through the two-zone design. The Symmetrix system connectsto two dedicated or isolated AC power lines. If AC power fails on one powerzone, the system continues to operate through the other power zone.

Symmetrix DMX-3 and DMX-4 systems have a modular power subsystemfeaturing a redundant architecture that facilitates field replacement of any of its components without any interruption in processing. The Symmetrix powersubsystem supports a (2N) power zone for redundancy and drive expansion.If any Symmetrix power supply fails, the remaining power supplies continueto share the load. The Symmetrix system senses the fault and reports it as an

environmental error.

The following section describes the power subsystem components for thesystem bays and storage bays.

DMX-3 and DMX-4 system bay

The system bay contains up to eight 1,800-watt power supplies that are splitinto two power zones (Power Zone A and Power Zone B) consisting of upto four power supplies each. The system bay also contains up to eight 2.2-kilowatt Battery Backup Unit (BBU) modules providing battery backup in theevent an AC failure occurs. One BBU provides the AC line power and high-voltage DC backup to one 1,800-watt power supply. The A-side BBU modulesreceive their power from the A-side Power Distribution Unit (PDU), and theB-side BBU modules receive their power from the B-side PDU.

Two Power Distribution Panels (PDPs), one for each zone, provide acentralized cabinet interface and distribution control of the AC power input



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lines when connected to the system bay PDUs. The PDPs contain the manualOn/Off power switches, which are accessible through the rear door.

Two Communications and Environmental Control (XCM) modulescommunicate with the system bay BBU modules to determine the BBU statusand run battery tests. The XCMs monitor and log environmental events acrosscritical components and report any operational problems. Critical componentsinclude global memory directors, power supplies, fans, and various on/off switches. The XCM environmental control is capable of monitoring eachcomponent’s local voltages ensuring optimum power delivery. Temperature of global memory directors is also continuously monitored.

Figure 1 illustrates the Symmetrix DMX-3 and DMX-4 system bay.

*The Service Processor consists of the KVM and the server.**The Battery Backup Unit Assembly consists of tow Battery Backup Unit Modules.

Figure 1. Symmetrix DMX-3 and DMX-4 system bay



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DMX-3 950 and DMX-4 950 system bay Two 1800-watt redundant power supplies located at the front of the card cage

enclosure supply the power to the card cage enclosure. The back of each driveenclosure contains two 12-volt power supplies (power and cooling modules)and two link control cards (LCCs). The two 12-volt power supplies (PS A, PSB) provide power and cooling to each drive enclosure. Each LCC (LCC A, LCCB) supports and controls one Fibre Channel loop and monitors the driveenclosure environment. The 2.2-kilowatt BBUs provide redundant backup forevery four drive enclosures. Two BBU modules also provide redundant power

backup to the card cage enclosure.

The PDU, when connected to the PDP, provides a means of connecting ACinput power to the system components from the independent power sources.The PDP provides a centralized cabinet interface and distribution control of theAC power input line when connected to the PDU. Each PDP contains a manual

On/Off power switch, which is accessible through the rear door.The physical connection to a Symmetrix system channel interface occurs at theconnectors on the front-end/back-end (FEBE) boards. The FEBE boardprovides an interface between the director and host channels. Additionally, thedirector boards monitor the card cage enclosure chassis environmentals PS1and PS2 and the fan module through the FEBE boards.

Figure 2 illustrates the Symmetrix DMX-3 950 and DMX-4 950 system bay.

Figure 2. Symmetrix DMX-3 950 and DMX-4 950 system bay



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Storage bay

The storage bay power subsystem consists of the drive enclosure power

supply/cooling modules and the BBU modules that provide the battery backupfor the drive enclosures. The 2.2-kilowatt BBUs provide redundant backup forevery four drive enclosures. The A-side BBU modules receive their power fromthe A-side PDU and support both the A- and B-side drive enclosures. The B-side BBU modules receive their power from the B-side PDU and support boththe A- and B-side drive enclosures. The back of each drive enclosure alsocontains two LCCs. Each LCC (LCC A, LCC B) supports and controls one FibreChannel loop and monitors the drive enclosure environment.

Two PDPs, one for each zone, provide a centralized cabinet interface anddistribution control of the AC power input lines when connected to the storage

bay PDUs. The storage bays PDPs contain the manual On/Off power switches,which are accessible through the rear door.

Figure 3 illustrates the storage bay.

Figure 3. Storage bay

Further information on the power subsystems is available on Powerlink.



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Power Vault overview




The Power Vault environmental algorithm continuously monitors the system’savailable power sources, available vault devices, and the battery holdup time inorder to determine three status values: Ability to vault (ATV), Need to vault(NTV), and Need to power down (NTPD). These status values, the Vault Saveoperation, and the Vault Restore operation are explained in the followingsections.

Power Vault operations

Vaulting operations are divided into two categories:

• Save operation – Saving global memory to the vault disks.

• Restore operation – Restoring global memory from the vault disks.

The following sections describe these operations in more detail.

Power Vault save operation

When a system is powered down, transitioned to offline, or whenenvironmental conditions trigger a vault situation, a Power Vault saveoperation is initiated. The part of global memory being saved first reaches aconsistent image (no more writes). The disk directors then write theappropriate sections of global memory to the vault disks, saving two copies of the logical data.

The BBU modules automatically transition to battery backup when theSymmetrix system detects loss of AC power. The BBU modules maintain powerto the Symmetrix system for up to 5 minutes while the global memory isvaulted to the vault disk drives.

When the disk directors are done writing to the vault disks, the system eitherfinishes powering off or remains in the offline state if it doesn’t need to poweroff.

Power Vault restore operation

When the Symmetrix system is powered on, the startup program does thefollowing:

• Initializes the hardware and the environmental system

• Restores the global memory from the saved data while checking the

integrity of the data

• Performs cleanup, data structure integrity, and reinitialization of neededglobal memory data structures



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At the end of startup program, the system resumes normal operation when theBBUs are recharged enough to support another vault save. The system will notcome back online until the BBU modules have a minimum of 300 seconds of

holdup time.

If any condition is not safe, the system will not resume operation and will callthe EMC Customer Support Center for diagnosis and repair. In this state, EMCCustomer Support will be able to communicate with the Symmetrix system andfind out the reason for not resuming normal operation.

Note: A fully charged BBU will have 600 seconds of charge time, enough tosupport two vault save operations.

Ability to vault (ATV)

There must be enough vault devices available to save one full copy of global

memory to disk. Enginuity™ will allow for the loss of a predetermined amountof vault devices depending on the configuration. If the minimum requiredvalue is reached, the system will begin to vault.

Need to vault (NTV)

The following is a list of conditions that will initiate a vault save operation:

The disk directors are taken offline

Loss of a sufficient amount of vault drives

Loss of a sufficient amount of disk directors

Insufficient battery holdup time

Loss of a sufficient amount of power supplies

Loss of AC power to both power zones

Loss of AC power to one power zone with insufficient battery holdup timeremaining on the opposite zone

Please note that multiple component failures within a zone are handleddifferently than a complete zone failure. If power is lost to an entire zone, thesystem will not begin to vault. However, if a single zone encounters multiplecomponent failures that reduce the number of operational power supplies to aninsufficient value, then the system will begin to vault. In general, the systemwill vault if half of the SPS modules in the system bay fail. This needs to betaken into consideration especially with smaller 24-slot systems (DMX-3 1500

and DMX-4 1500).

For example, a minimum configuration DMX-4 1500 is required to have onlytwo SPS modules configured per zone in the system bay. But the system will

begin to vault if two SPS modules fail in a single zone. A system with this



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configuration will also begin to vault if each zone were to lose a single SPS as both zones would have lost redundancy.

Note: Systems with this type of configuration can be upgraded withadditional SPS modules and power supplies to avoid these situations.

Six-slot systems (DMX-3 950 and DMX-4 950) have fewer components in thesystem bay and are essentially protected only by the other zone. Therefore,these systems will not need to vault until both zones experience a failure.

Need to power down (NTPD)

The system will need to power down after performing the vault save operationif the system loses AC power to both power zones. The power subsystem’stwo-zone design ensures that if there is an AC power loss to one of the zones,power from the second power source maintains power to the affected bay or

bays, provided that each system bay or storage bay’s two PDPs are connectedto two separate source PDUs at the customer’s site.

84,VALT,PRMS command

The 84,VALT,PRMS command, shown in Figure 4, displays the followinginformation:

Power Sources – Minimum required, configured count, and currentcount.

Vault Drives – Minimum required and capacity count. The capacitycount will decrement if a drive that contains vault devices were to fail.

NTV – A value of 0 indicates the system does not need to vault. Avalue of 1 indicates the system needs to vault.

ATV – A value of 0 indicates the system does not have the ability tovault. A value of 1 indicates the system has the ability to vault.

NTPD – A value of 0 indicates the system does not need to powerdown. A value of 1 indicates the system needs to power down.



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Best practices for site and system service activities



Figure 4. Inlines command 84,VALT,PRMS


Power Vault is designed to maintain data integrity when the system needs to be taken offline or powered down manually. Environmental conditions mayalso trigger the system to begin a vault save operation. This must be consideredwhen performing system and site power maintenance.

The following sections describe best practice recommendations for customersand EMC service personnel to follow while performing power maintenanceactivities. Configuration options and rules as well as powerdown and powerupprocedures are also discussed.

Best practices for customers during site PDU maintenance

It is highly recommended that EMC Customer Service field personnel are on

site prior to and during any power maintenance activity. EMC CustomerService field personnel have access to commands and tools to check for propersystem health status.



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It is also highly recommended that EMC Customer Service field personnel andsite electricians verify that the AC power feeds to each rack of equipment comefrom redundant power sources/PDUs prior to beginning any power-related

maintenance.The following guidelines should be followed by customer site personnel toavoid accidentally causing the system to vault while performing sitemaintenance:

• Verify system health status prior to beginning any power-relatedmaintenance.

• Discuss power maintenance plans with the local EMC Customer Servicefield team prior to activity.

• Have the local EMC Customer Service field team verify the Power ZoneTask is disabled before beginning maintenance. The “Power Zone Task”section on page 26 provides more information.

• When installing a new system, apply power from two separate sourcePDUs at the site to each bay’s two PDPs. The Physical Planning Guides foreach specific model provide additional details and are also available onPowerlink.

• Before beginning any power maintenance on site or on previously installedsystems, verify that each bay’s PDPs are connected to separate sourcePDUs.

• Configure power redundantly to ensure that any PDU shutoff will not takepower away from both power zones of any bay.

• If power has been removed from any bay’s zone more than once, or if

power has been removed from any combination of zones, do not removepower from the other zone until adequate battery recharge time has passedon the discharged BBUs. Battery charge time must be greater then 300seconds on the SPSs to support at least one vault save if needed. Chargetime typically takes a minimum of 2 hours.

Note: Enginuity 5773 introduces a Battery Conservation algorithm that willshut off the SPS modules in a zone that loses AC power as long as theopposite zone is fully operational. This helps prevent the SPS modules from

being completely drained during a single-zone power failure. The loss of power to the zone will still drain the SPS modules of some battery capacity,

but it increases the amount of single-zone power outages that can beexperienced before the SPS modules drop below 300 seconds of holdup time.

This functionality is also targeted for a future release of 5772 code.

EMC Customer Service field personnel should perform the following steps toverify battery charge status:



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From the main SymmWin screen, select Tools > Environmental. Then, click the Health Check tab, and click Run Health Check, as shown in Figure 5.

Figure 5. Environmental GUI health check results: SPS problems detected



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If errors are present, click the Power System tab to view where the issueexists. Figure 6 shows sample results.

Figure 6. Power System tab: Enclosures with SPS battery charge less than 300 seconds



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The Inlines command for displaying the system bay SPS status is84,VALT,GPWR. Figure 7 shows a sample of the command output.

Figure 7. Inlines command 84,VALT,GPWR: System bay SPSs below 300 seconds battery chargetime

The Inlines commands to display the storage bay SPS status are more tedious.The preferred method is via the Environmental GUI.

Best practices for EMC service personnel

The following guidelines should be followed by EMC service personnel toavoid accidentally causing the system to vault while performing system or sitemaintenance:

• Prior to starting any work, ensure that the power feeds to enclosures comefrom redundant sources.

• Ensure that DMX internal cable verification tests have been done.

• Verify the Power Zone Task is disabled before beginning maintenance. The“Power Zone Task” section on page 26 provides more information.



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• Run a health check before power activity.

• Before removing power from a zone, check that opposite zone has allpower supplies on without faults.

• Before beginning any maintenance, check the SPS health. If previouslyunknown failures are found, contact EMC Customer Support Center forassistance.

Perform the following steps to verify SPS health:

From the main SymmWin screen, select Tools > Environmental. Then,click the Health Check tab, and click Run Health Check.

Figure 8 shows a faulty SPS in the system bay.

Figure 8. Environmental GUI health check results: SPS not ready in system bay



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Click the Power System tab to identify the faulty component, as shown inFigure 9.

Figure 9. Power System tab: SPS 4B not ready in system bay



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The Inlines command to display system bay SPS status is 84,VALT,GPWR.Figure 10 shows sample output.

Figure 10. Inlines command 84,VALT,GPWR: System bay SPS status



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Figure 11 shows a faulty SPS in the storage bay.

Figure 11. Environmental GUI health check: SPS not ready in storage bay



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If errors are present, click the Power System tab to view where the issueexists. Figure 12 shows sample results.

Figure 12. Power System tab: SPS not ready in storage bay

The Inlines commands to display BBU status and power for the storage bayare more complex; the preferred method is via the Environmental GUI.



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• Each BBU provides power to four disk-array enclosures (DAEs). Ensurethat all four DAEs on opposite sides are healthy before maintenance. If previously unknown failures are found, contact the EMC CustomerSupport Center for assistance.

Perform the following steps to verify DAE health:

From the main SymmWin screen, select Tools > Environmental. Then,click the Health Check tab, and click Run Health Check, as shown inFigure 13.

Figure 13. Environmental GUI health check results: DAE SPS problems detected



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• Check the battery test history along with charge state status before doingany maintenance. Perform the following steps to verify battery test history:

From the main SymmWin screen, select Tools > Environmental. Then,click the Power System tab, and click the Battery Test tab, as shown inFigure 15.

Figure 15. Battery test history

If there is a failure, press F7 to refresh the display. If the failure remains,contact the EMC Customer Support Center for assistance.



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• Whenever an action is taken on a power component, ensure that NTV isnot set with the 6F,PLOG command (shown in Figure 16). A value of 1indicates the system needs to vault. If it is set, there is a 60-second window

to undo the action that set it.

• When removing disk drives that contain vault devices, check that the NTVdoes not get set with the 6F,PLOG command (shown in Figure 16). A valueof 1 indicates the system needs to vault.

Figure 16. Inlines command 6F,PLOG

Online DAE or disk drive upgrades

Do not connect any cables from the new DAEs/drive bays to the existingsystem until all SPS units in the new DAEs/drive bays are fully charged.

Ensure all SPS units in the new DAEs or new drive bays are fully charged priorto proceeding with the online upgrade. There should be no flashing green LEDs

on any SPS module. Normal charge time is 2 hours minimum.

Furthermore, do not power down any drive bays that are installed even if thedisk drives in the bay are not yet configured.



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If there are any power or environmental issues in a daisy-chained environment,the vault devices that reside on that loop are discounted. If all the extendedloops have power events due to the low SPS charge status, then Enginuity will

discount all the drive loops and subsequently all the vault drives. If the numberof available vault drives falls below a predetermined level as set by Enginuity,the system will begin to vault.

Knowledgebase solution emc154235 provides more information.

Powerdown procedure

The Symmetrix contains no user-serviceable parts. Therefore, the system bayand storage bays should not be opened for any reason by untrained personnel.If the Symmetrix is in need of repair, only qualified personnel familiar withsafety procedures for electrical equipment and the Symmetrix should accesscomponents inside the unit.

Note: The Symmetrix is designed to stay powered up for most all situations.Unless there is an emergency situation, first call the EMC Customer SupportCenter for assistance before powering down the Symmetrix.

The method that EMC Customer Service field personnel should use to powerdown the Symmetrix is to execute a script. In the Procedure Wizard underRTS/CEs Services, run the Sym Offline/Shutdown script. The script willensure that the system bay is powered down prior to the storage bays, or elsethe system may not be able to save the vault image.

The script instructs the service personnel to perform these steps to power downthe Symmetrix:

1. Stop all processes to the Symmetrix. Note: If you are powering down for an emergency condition, stopping all processesto the system is not necessary.

2. On the rear door of the system bay (Figure 17), press the Zone A and ZoneB PDP power switches to the down “O” OFF position.

3. On the rear door of the storage bays (Figure 17), press the Zone A and ZoneB PDP power switches to the down “O” OFF position.

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Figure 17. System bay and storage bay power switches

Powerup procedure

Note: Do not use the following procedures for powering up the Symmetrixfor the first time. If you have powered down the Symmetrix for an emergency

condition, call the EMC Customer Support Center for assistance beforepowering up the system.

Please reference the Physical Planning Guide and Quick Start PowerConnection Guide for your specific model for power connection andconfiguration requirements.

Perform these steps to power up the Symmetrix after it has been routinelypowered down by the PDP power switches:

1. On the rear door of each storage bay (Figure 17), press the Zone A andZone B PDP power switches to the up “I” ON position.

2. On the rear door of the system bay (Figure 17), press the Zone A and Zone

B PDP power switches to the up “|” ON position. The Symmetrix system begins its initial microcode program load (IMPL) startup procedure.

3. Wait at least 30 minutes for the IMPL procedure to complete.



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Note: The actual IMPL procedure time varies by system type andconfiguration.

Configuration options and rules

There are two Power Vault related options that can be configured to sitespecifications:

Power Vault Wait Time

Power Zone Task

All other configuration rules are strictly defined by Enginuity. The options andrules are discussed in the following section.

Power Vault Wait Time

The configuration file is customizable in order for the machine to be able tosurvive brownouts in areas where there are frequent power interruptions. Itcan be set for 1, 2, or 3 minutes to ride out temporary power interruptions.After that time, the front-end directors will be taken offline and the diskdirectors will begin the vault save.

The default setting is 1 minute. EMC Customer Service field personnel shoulddiscuss with the local Configuration RTS before attempting to make anychanges to this setting. The exact system configuration must be taken intoaccount before an increase to the wait time value is approved. The 3-minutevalue is an extreme case and is approved only in specific configurations.

The Power Vault Wait Time setting is in the IMPL Initialization screen underCommon Settings, as shown in Figure 18. An online configuration change must

be performed to commit the change to the system.

Figure 18. Power Vault Wait Time field in IMPL Initialization screen

Power Zone Task

The Power Zone Task is optional under normal operation. However, it is highlyrecommended and considered best practice that the local EMC CustomerService field team verifies this setting is disabled before beginning any power-related maintenance on the system and before the customer begins any power-



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related maintenance onsite. The task setting can be modified in the SymmetrixSite Configuration window, as shown in Figure 19. An online configurationchange is not required to change this setting.

Figure 19. Enable Power Zone setting in Symmetrix Site Configurationwindow

When the Power Zone Task is enabled and the system loses AC power to asingle power zone, a 20-hour timer is invoked. The system will call home tonotify the EMC Customer Support Center of the event. When the timer countsdown to 5 hours, the system will again call home. Before the 20-hour periodends, the EMC customer engineer can choose one of three options:

Repair the cause of the power fault.

Reset the 20-hour timer to continue the single power zone operation.

Allow the system to vault, shutting down the system in an orderly manner.

Knowledgebase solution emc130487 provides more information on the PowerZone Task.

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Conclusion



Vault device configuration rules

The following configuration rules apply to vault devices:

• 5 GB on the first four drives of every drive loop is reserved for memoryvaulting.

• Each disk director pair requires 32 such dedicated devices for a total of 160GB of vault space per disk director pair.

• The vault devices can only use single-mirror data protection and cannot beconfigured with TimeFinder®/Snap, virtual, or dynamic spare devices.

• The drive pool, virtual devices, or drive devices cannot reside in the 5 GBof vault space. However, they can reside on the same physical disk drive asthe vault devices but not within the vault devices.

• The distribution of the vault devices across the disk directors, the back-endinterfaces, and the physical disks should be such that a full vault save will

be possible within the time frame dictated by the capacity of the battery (upto 5 minutes).

• The total capacity of all of the vault hypervolumes in the system will be atleast sufficient to keep two logical copies of the persistent part of globalmemory.

• Physical drives that contain vault devices are candidates for permanentsparing if the following is true for each model:

• On the DMX-3, if there is an available spare on the same primary loop

• On the DMX-4, if there is an available spare on the same disk director

processor

Conclusion

This technical note explained Power Vault operations, described hardwarefeatures and environmental monitoring, and recommended best practices forperforming power maintenance. More information is provided in the“References” section on the next page.



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References



References

DMX-3

Symmetrix DMX-3 Product Guide

Symmetrix DMX-3 Physical Planning Guide

Symmetrix DMX-3 Quick Start Power Connection Guide

DMX-3 950

Symmetrix DMX-3 950 Product Guide

Symmetrix DMX-3 950 Physical Planning Guide

Symmetrix DMX-3 950 Quick Start Power Connection Guide

DMX-4

Symmetrix DMX-4 Product Guide

Symmetrix DMX-4 Physical Planning Guide

Symmetrix DMX-4 Quick Start Power Connection Guide

DMX-4 950

Symmetrix DMX-4 950 Product Guide

Symmetrix DMX-4 950 Physical Planning Guide

Symmetrix DMX-4 950 Quick Start Power Connection Guide

Other

Knowledgebase solution emc119567 – “What is the correct power ON/OFF sequence for theSymmetrix DMX-3?"



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References



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