Welcome to PowerPath Foundations

Transcription

1 IMPACT Home IMPACT modules consist of focused, in-depth training content that can be consumed in about 1-2 hours Welcome to PowerPath Foundations Course Description Start Training Run/Download the PowerPoint presentation Student Resource Guide Training slides with notes Assessment Must be completed online (Note: Completed Assessments will be reflected online within hrs.) Complete Course Directions on how to update your online transcript to reflect a complete status for this course. For questions or support please contact Global Education 2004 EMC Corporation. All rights reserved.

2 IMPACT Course Completion Link to Knowledgelink to update your transcript and indicate that you have completed the course. PowerPath Foundations Course Completion Steps: 1. Logon to Knowledgelink (EMC Learning management system). 2. Click on 'My Development'. 3. Locate the entry for this learning event you wish to complete. 4. Click on the complete icon [ ]. Note: The Mark Complete button does not apply to items with the Type: Class, Downloadable (AICC Compliant) or Assessment Test. Any item you cancel from your Enrollments will automatically be deleted from your Development Plan. Click here to link to Knowledgelink For questions or support please contact Global Education Back to Home 2004 EMC Corporation. All rights reserved.

3 PowerPath Foundations IMPACT Course Description e-learning This foundation level course provides participants with an Course understanding of how EMC PowerPath is used to improve Number: MR-WP5-PWRPFD performance and increase availability as part of EMC s Technology Foundations. Method: IMPACT Duration: 1 hour This course is part of the EMC Technology Foundations curriculum and is a pre-requisite to other learning paths. Audience This course is intended for any person who presently or plans to: Educate partners and/or customers on how EMC PowerPath can maximize availability and performance in a Symmetrix and CLARiiON-based storage infrastructure Provide technical consulting skills and support for EMC products Analyze a Customer s business technology requirements Qualify the value of EMC s products Collaborate with customers as a storage solutions advisor Prerequisites Prior to taking this course, participants should have completed the following Courses: None Course Objectives Upon successful completion of this course, participants should be able to: Discuss the features and benefits of PowerPath in an open systems host environment Explain how PowerPath achieves transparent recovery List the environments that PowerPath supports Modules Covered This course includes one module: PowerPath Foundations Labs Labs reinforce the information you have been taught. The labs for this course include: None Assessments This course includes a self-assessment quiz to be conducted on-line via KnowledgeLink, EMC s Learning Management System. If you have any questions, please contact us by at GlobalEd@emc.com Page 1 of 1

4 PowerPath Foundations, 1 PowerPath Foundations 2004 EMC Corporation. All rights reserved. 1 Welcome to PowerPath Foundations. EMC PowerPath is a server-resident software product that provides application availability when a SCSI I/O channel or Fibre Channel path fails. It also improves a servers ability to handle heavy storage I/O loads.

5 PowerPath Foundations, 2 EMC Technology Foundations EMC Technology Foundations consists of AutoIS, SAN products, NAS products, and Storage Platforms, as well as advanced storage management software. EMC Technology supports the portfolio of end-to-end services designed to help accelerate the implementation of Information Lifecycle Management (ILM). ILM uses EMC Technology to enable organizations to better and more cost-effectively manage, properly protect, achieve compliance and improve the availability of their business information in a way that ties varying information usefulness to business goals and service levels EMC Corporation. All rights reserved. 2 This course describes PowerPath and its features that contribute to EMC Technology Foundations.

6 PowerPath Foundations, 3 Course Objectives After completing this course, you will be able to: Discuss the features and benefits of PowerPath in a server environment Explain how PowerPath achieves transparent recovery List the environments that PowerPath supports Describe the management functions available using the GUI and CLI interface 2004 EMC Corporation. All rights reserved. 3 These are the objectives for this training. Please take a moment to read them.

7 PowerPath Foundations, 4 PowerPath - Introduction Server based software Most Unix Hosts NT/W2K Each Logical Volume can be configured with up to 32 paths from the storage system to the host Automatic and non-disruptive path failover eliminates, cable,channel director or ESN component as single point of failure Automatic load balancing over all available paths can improve performance Host Components Host Applications EMC 2 PowerPath Device Layer Symmetrix and CLARiiON 2004 EMC Corporation. All rights reserved. 4 PowerPath is server-resident, performance and information availability enhancing software solution. It combines multiple path I/O capabilities, automatic load balancing, path failover, and logical volume management functions into one integrated solution. Automatic: PowerPath uses sophisticated algorithms to increase application I/O rates through Symmetrix and CLARiiON with automatic data path load balancing allowing for greatest efficiency and throughput. PowerPath s volume manager capability simplifies disk administration tasks to further reduce total cost of ownership through high-level commands that hide storage complexity. It automatically manages workloads and volume expansion. Automatic path failover By taking advantage of all paths, PowerPath increases the ability of server access to data on the Symmetrix and CLARiiON arrays. PowerPath moves I/O workloads across multiple paths to ensure fastest possible I/O speed. Non-disruptive: PowerPath provides users application to storage automation, seamless data migration, and automatic import of Volume Groups, and simplifies the growth of logical volumes while application remain online. PowerPath optimizes server and data path utilization by avoiding downtime. Optimized: By leveraging your server, SAN, and storage assets, PowerPath maximizes your investment by increasing storage utilization. Dynamic load balancing When the host needs access to data on the Symmetrix or CLARiiON, PowerPath uses the quickest and easiest route or path to access the data. PowerPath supports several load balancing policies compared to other vendors. In the rare instance of a path failure, PowerPath will re-issue I/O to an alternate path maintaining data availability and ensuring information access. PowerPath offers policy-based dynamic path management that accelerates information access and provides high availability.

8 PowerPath Foundations, 5 PowerPath Features Automatic path failover Dynamic load balancing Logical Volume Manager Automatic detect and restore of failed components Online configuration and management Common driver support across Symmetrix and CLARiiON Write throttling Consistency Group support (Symmetrix only) 2004 EMC Corporation. All rights reserved. 5 Other attributes, in addition to Automatic path failover and dynamic load balancing include: Integrated Logical Volume manager that provides a logical abstraction of storage. Automatic detect and restore of failed components For example, if a cable is mistakenly dislodged, PowerPath will take all existing I/O that was going down that particular path and re-route it to another active path. Once the cable is re-attached, another feature of PowerPath, called Auto Restore, automatically restores path access permitting data flow down the path again. Online configuration and management You can have some paths active and some passive (or "standby"). This means that the passive paths will only be used if the active paths fail. A user can segment applications; for instance, segment logs from table spaces, or segment one application from another. For example, in an eight-path configuration running two applications, you can have each path active for one application and passive for the other. PowerPath allows the user to make configuration changes while applications remain online, meaning you can reconfigure the load balancing policy, take paths offline and online, hot repair, etc. PowerPath also supports common driver connectivity on the Symmetrix and CLARiiON, which means that one host can share the same to both Symmetrix and CLARiiON arrays. PowerPath also supports write throttling, which is a way to way to minimize or eliminate database read timeout errors, by throttling the write so that a read can be processed. For a group of Symmetrix devices, PowerPath will maintain the integrity of a database distributed across multiple SRDF units. PowerPath also supports the ability of booting from a mirrored R2 device in an SRDF configuration.

9 PowerPath Foundations, 6 Path Fault without PowerPath In most environments a host will have multiple paths to the Storage System Volumes are spread across all available paths Each volume has a single path Host adapter and cable connections are single points of failure Work load not balanced between all paths SERVER STORAGE Host Application(s) Interconnect Topology Storage SCSI Driver Host Bus Adapter 2004 EMC Corporation. All rights reserved. 6 Without PowerPath or another path failover software package, the loss of a channel (red dotted line) means one or more applications may stop functioning. This can be caused by the loss of a Host Bus Adapter, Symmetrix Channel Director, CLARiiON Storage Processor, FC-AL hub, or a failed (kicked) cable. In a standard non-powerpath environment, these are all single point of failure. In this case, all I/O that was heading down the path highlighted in red is now lost, resulting in an application failure and the potential for data loss or corruption.

10 PowerPath Foundations, 7 PowerPath Configuration All Volumes are accessible through all paths Applications direct IO to PowerPath PowerPath directs I/O to optimal path based on current workload and path availability SERVER STORAGE Host Application(s) PowerPath Interconnect Topology Storage SCSI Driver Host Bus Adapter 2004 EMC Corporation. All rights reserved. 7 Without PowerPath, if a host needed access to 40 logical volumes, and you had four host bus adapters, you would most likely set it up so that 10 volumes were presented to each host bus adapter. With PowerPath, you would set it up so that all 40 volumes could be Seen by all four host bus adapters. This would require: The storage system be configured to present the volumes to multiple front-end ports The SAN fabric is zoned Access control through Volume Logix or Storage Logix binding (if needed) If set up properly, each Logical volume would be presented multiple times. For example, in a Solaris environment, if SLV 001 is presented to four different front-end directors, and the fabric is zoned properly, that single volume may actually have four different logical device file names. I.e. /dev/dsk/c1t0d0, /dev/dsk/c2t0d0, /dev/dsk/c3t0d0, /dev/dsk/c4t0d0. While this may be somewhat confusing the first time you see this, PowerPath understands that the four device files actually al point to a single volume and will direct the I/O appropriately.

11 PowerPath Foundations, 8 Transparent Recovery with PowerPath If a host adapter, cable or channel director/storage Processor fails, the device driver returns a timeout to PowerPath PowerPath responds by taking the path offline and re-driving I/O through an alternate path Subsequent I/Os use surviving path(s) Application is unaware of failure SERVER STORAGE Host Application(s) PowerPath Interconnect Topology Storage SCSI Driver Host Bus Adapter 2004 EMC Corporation. All rights reserved. 8 PowerPath provides transparent recovery in response to a path failure. PowerPath will ensure that the I/O heading down the failed path is re-directed (keeping in mind load characteristics and priorities) to the most suitable alternative path. Unlike other path management products that will failover all I/O to the next available path (overburdening the path), PowerPath uses intelligence to decide where to failover the I/O. Because PowerPath spreads the additional load across the remaining channels, the system will continue to operate, however, in a degraded mode. This takes the pressure off the staff to make corrections immediately. Since some O/S servers do not support hot plugging of boards, so the replacement of an may require bringing the server down, PowerPath allows the IT staff to schedule the repair at a convenient time. If you are concerned with degraded mode behavior, the PowerPath GUI provides the ability to disable and re-enable channels on the fly so you can test the performance sensitivity of your configuration. Simple channel failover products work in pairs, i.e., one channel is the backup for the other. In the diagram, two pairs of channels would be set up. If one channel fails, all load for that channel goes to its twin, essentially doubling its load. With PowerPath, the load is spread across the three remaining channels. The objective is to make channel failover a non-issue. There are low cost products that provide two channel failover. By making queue management the issue, PowerPath is not competing with channel failover products and establishes the value of the PowerPath solution. The ability to compensate for a lost channel by spreading the I/Os across multiple channels instead of dumping all of it on one requires multi-channel support.

12 PowerPath Foundations, 9 I/O without PowerPath Queues Out of Balance I/O performance is partially based on queue length Optimal performance cannot be achieved unless work is balanced I/O workload across s is seldom balanced Any any point in time some paths may be idle while other paths have multiple I/O operations queued SERVER Host Application(s) SCSI Driver Host Bus Adapter Storage 2004 EMC Corporation. All rights reserved. 9 The server views each disk resource to be on a single path. EMC technical personnel set up the configuration of the storage system to spread I/O load across the paths. Each application is set up with its own storage. The storage is allocated to Channel Directors or Storage Processors based on expected data requirements of the applications. This setup is done based on snapshot measurements, guesstimates of average loading and predictive loads, and the experience of the EMC experts. This diagram depicts a snapshot of the system at a moment in time. The depth of the I/O queues is very unbalanced. Host applications sitting on top of deep queues are not getting the data they need. If this was the average loading, the System Administrator would reconfigure the system to balance the load better. In any system, there will be points in time when the load is unbalanced due to one application receiving heavy I/O requirements. In this instance, two of the applications are currently causing high I/O traffic. At this point, two channels are overloaded (depicted by the red disks on the outside, and the pending request stack) while two other channels are lightly loaded. In a while, the requests will have been handled and the system will return to a more balanced load. In the meantime, the applications are being data starved and the users or applications are experiencing less than optimal performance.

13 PowerPath Foundations, 10 I/O with PowerPath Queues in Balance PowerPath dynamically balances workload across all available paths PowerPath will provide greatest improvement in performance in environments where the workload is not balanced Workloads are seldom balanced Workloads dynamically change SERVER STORAGE Host Application(s) PowerPath Interconnect Topology SCSI Driver Host Bus Adapter 2004 EMC Corporation. All rights reserved. 10 With PowerPath in the system, applications transparently access PowerPath instead of the (SCSI driver) devices. PowerPath allocates the requests across the available channels, reducing bottlenecks and improving performance. This diagram shows a similar snapshot with PowerPath using multiple channels to minimize the queue depth on all channels. Since the Channel Directors or Storage Processors are writing to cache and not to disks, any Channel Director/Storage Processor can handle any request. This allows PowerPath to constantly tune the server to adjust to changing loads from the applications running on the server. PowerPath improves the performance of the server, enabling it to make better use of the storage. This results in better application performance and less operational resources spent on the care and feeding of the system, and more (financial) value from your server investment. PowerPath does not manage the I/O queues; it manages the placement of I/O requests in the queue.

14 PowerPath Foundations, 11 Performance Tuning and Active / Standby Channel Policies Host Application A Host Application B Standby Paths Application A Channel Group SERVER SCSI Driver Host Bus Adapter PowerPath Standby Paths Application B Channel Group SCSI Driver Host Bus Adapter STORAGE Cache Available bandwidth can be segmented per application 2004 EMC Corporation. All rights reserved. 11 PowerPath provides configuration flexibility that allows you to define some paths active and some passive or "standby". This means that the passive paths will only be used if the active paths fail. You can dynamically add and remove paths. For example, if you had eight paths partitioned into four for one application and four for another, and one application needed more bandwidth, say during batch, you can, through scripts, add more paths during the batch run and take them away when you're done. The actual command is powermt set mode=standby/active adapter=adapter# dev=integer/all Here are examples of two practical applications of this: If you have two applications on a server that are both very busy, but you don t want the activity of one application to impact the performance of the other application, you could set up the two applications to have their own sets of channels. I/O for those two channels would be balanced among the channel groups only, and if one application was very busy, the other application would not be impacted from an I/O standpoint. In the event of all the defined channels for one Channel Group failing, I/O would be re-routed to the other Channel Group s channels. If a host has two types of channels, for example, Fibre Channel and SCSI, you would have to segregate channels by channel type. It is not possible for PowerPath to load balance an application across both Fibre Channel and SCSI together, but by using channel segregation, a user can set up the environment so that PowerPath would load balance across the SCSI channels for one set of devices and Fibre Channel for the other set of devices. Then, in the event of a failure, all the devices defined to the failed paths would use the other available paths for I/O, because they were standby paths for those devices.

15 PowerPath Foundations, 12 PowerPath Load Balancing Policies Symm_opt / CLAR_opt (default) I/O requests are balanced across multiple paths based on composition of reads, writes, and user-assigned device / application priorities Round_Robin I/O requests are distributed to each available path in turn Least_I/Os I/O requests are assigned to the path with the fewest number of requests in the queue Least_Blocks I/O requests are assigned to the path with the fewest total blocks in the queue Path failover only No Redirect Disable path failover and load balancing (same as Transparent=on) Default for Symmetrix when there is no license key; not supported on CLARiiON Basic Failover CDE-type functionality (SPA SPB failover) Default for CLARiiON when there is no license key; not supported on Symmetrix 2004 EMC Corporation. All rights reserved. 12 The Symm_opt/CLAR_opt policies Choose paths based on path load and logical device priority. Device priority is host based priority and not Symmetrix/CLARiiON level priority. Round Robin I/O requests are assigned to each available path in rotation. Least I/Os Load balance is based on the number of pending I/Os. I/O requests are routed to the path with the fewest queued requests, regardless of total block volume. Least Blocks Load balance is based on the number of blocks in pending I/Os. I/O requests are routed to the path with the fewest queued blocks, regardless of the number of requests involved. For native devices, this policy uses the path that would have been used if PowerPath were not installed. For pseudo devices, it uses one arbitrary path for all I/O. For all devices, path failover is in effect, but load balancing is not. No Redirect Neither load balancing or failover is in effect. If this algorithm is set on a failed path and a native device is used, I/O errors will occur when I/O is directed to that path. This policy is valid only on Symmetrix arrays. Basic failover Load balancing is not in effect. I/O routing on failure is limited to one host bus and one port on each Storage Processor. This policy is required for a non-disruptive upgrade. It protects against Storage Processor and back-end failures, but not against or host loop failures. PowerPath is required to prevent and/or host loop failures. You can change the policies from the powermt set policy command, or within the GUI on Windows.

16 PowerPath Foundations, 13 Active-Active vs. Active-Passive CLARiiON s LUN Ownership Model CLARiiON backend employs dualport disks, redundant FC-AL loops All disks have paths to both Storage Processors CLARiiON LUNs are owned by one Storage Processor One Storage Processor services I/O for LUN Second path to LUN is passive Host Director Director Host Switch Port Port Cache SCSI disk SCSI disk SCSI disk Switch Port Port Director Symmetrix * Symmetrical Volume Access: volume accessible (active) on all paths Cache Host Storage Processor Host Switch Port Port CMI State Info SCSI disk SCSI disk SCSI disk Switch Port Port Cache Storage Processor CLARiiON * Asymmetrical Volume (LUN) Access: LUN accessible (active) on one Storage Processor at a time 2004 EMC Corporation. All rights reserved. 13 Architecturally, the Symmetrix supports an Active-Active access in that the same LUN can be presented and is accessible simultaneously through multiple front-end ports. The CLARiiON uses a LUN ownership concept where a LUN is owned by on storage processor at a time. In the diagram above, there are four available paths to the CLARiiON on this host. PowerPath enhances CLARiiON high availability with I/O path failover software. During normal operations, the host utilizes two high-speed data paths. In the event of a failure of a, Storage Processor, or cable, PowerPath automatically reroutes traffic in seconds. By taking advantage of both paths under normal conditions, PowerPath increases the availability of the server to access data on the CLARiiON. All this is accomplished while the application remains online.

17 PowerPath Foundations, 14 Failover Redefined with PowerPath Use all active paths before doing a trespass When all active paths are exhausted, trespass on a LUN by LUN basis Scope of LUNs failing over depends upon component If there is a failure to an or cable connecting the to a Storage Processor, hub, or switch, just the affected host s LUNs fail over If there is a failure to a Storage Processor, all LUNs assigned to that Storage Processor will fail over if they are accessed 2004 EMC Corporation. All rights reserved. 14 Failover occurs on a LUN-by-LUN basis. This helps avoid any unnecessary trespassing of devices that can cause possible performance issues and degradation. A multi-path failover will re-route the I/O through an alternate path to the LUN through the Storage Processor that is the primary owner. If the LUN is still inaccessible after going through all possible paths, a LUN trespass will occur. Trespass means that LUN ownership has been transferred to the alternate Storage Processor. The manner in which logical units fail will also depend upon the mode of failure within the data path. If there is a failure of the, or anywhere between the server and the array, just the affected host s devices would trespass over to the other Storage Processor, so they are accessible to the server through the alternate data path. If there is a Storage Processor failure, all devices assigned to that Storage Processor that received I/O from the requesting host will fail over to the surviving Storage Processor.

18 PowerPath Foundations, 15 PowerPath Failover with CLARiiON Path Fault Fault Storage Processor Fault Application Application PowerPath Interconnect Topology SP-A CLARiiON SP-B 2004 EMC Corporation. All rights reserved. 15 PowerPath protects the customers environment in case of a path,, or Storage Processor failure. Path fault If a path or a cable is accidentally bumped or pulled, PowerPath will automatically fail over the path to an alternate path. Once the path(s) have been restored, PowerPath automatically recognizes this and resumes sending I/O down those paths. fault If an is lost at the front end, PowerPath will fail over the entire path to an alternate. Once the is brought back online, PowerPath recognizes this and resumes sending I/O through the alternate. Storage Processor fault If a SP-B fails (in diagram), PowerPath will stop all I/O that was currently headed from the server to SP-B and trespasses it over to SP-A; once SP-B is brought back online, PowerPath recognizes that SP-B is now available and resumes sending I/O down to SP-B. In the event of any of the above scenarios taking place, PowerPath ensures that applications remain continuously available.

19 PowerPath Foundations, 16 PowerPath Load Balancing with CLARiiON LUN Ownership Model with CLARiiON Load balancing Load balancing and failover across active channels Trespass to passive channels in event of all paths / Storage Processor failover Only on systems with two or more FC-SW (CLARiiON FC4700 and above) ports per Storage Processor For s on active paths only Not across Storage Processors Customer selects best algorithm for application requirements CLAR_opt is usually recommended 2004 EMC Corporation. All rights reserved. 16 Why active and passive paths? The reason the CLARiiON LUN ownership model. The LUN ownership model means that only one Storage Processor can own a particular LUN at any one time. For the other Storage Processor to gain access to the LUN, it must take ownership of the LUN. Some people describe this as active-passive (on active-passive storage systems, available paths are those paths leading to the active Storage Processor for each logical device). However, there can be many LUNs on a CLARiiON and each of these LUNs can be assigned to either Storage Processor. PowerPath can distribute the I/O for all logical devices over all paths shared by those logical devices, so all paths are equally burdened. PowerPath load balances I/O on a host-by-host basis. It maintains statistics on all I/O for all paths. For each I/O request, PowerPath intelligently chooses the least-burdened available path, depending on the load balancing and failover policy in effect. If an appropriate policy is specified, all paths in a PowerPath system have approximately the same work load. If no preference is given, PowerPath will choose what it thinks is the best method of load balancing.

20 PowerPath Foundations, 17 PowerPath / CLARiiON (CDE Functionality) Provides back-end failover, non-disruptive upgrades, and single configuration support for single-attach hosts Is included in CLARiiON Utility Kit Access Logix is required Non-HA environment No multi-pathing capabilities Application PowerPath Fibre Channel Switch SP-A CLARiiON SP-B 2004 EMC Corporation. All rights reserved. 17 As a special case for non-high availability environments, PowerPath replaces CDE (CLARiiON Driver Extensions) functionality. It is provided on all CLARiiON arrays, and provides single configuration support, back-end failover support, and non-disruptive upgrade support. This does not have any multi-pathing or load balancing capabilities and should not be used in a high availability environment.

21 PowerPath Foundations, 18 PowerPath and HA Clusters PowerPath enhances High Availability Cluster environments Increases application availability by eliminating the need to fail over when a path failure occurs Tested with leading HA cluster products HACMP for AIX HP MC ServiceGuard Veritas FirstWatch Sun Cluster Qualix HA NT MSCS SERVER STORAGE Application PowerPath SERVER Interconnect Topology Application PowerPath 2004 EMC Corporation. All rights reserved. 18 Open Systems clustering technology manages application availability by detecting failures and restarts high availability applications on a surviving cluster node. The deployment of PowerPath in the cluster eliminates the application downtime due to a channel failure. PowerPath will detect the channel failure and use alternate channels so that the cluster software does not have to reconfigure the cluster to keep the applications running. PowerPath improves the availability of the applications running in the cluster. Many clusters are deployed to provide performance scalability (i.e., Oracle Parallel Server). PowerPath s load balancing can help the customer maximize performance and get the greatest value from their cluster investment. PowerPath must work cooperatively with the cluster software. This does not require special code in the cluster, but does require PowerPath to work with storage management component of the cluster software. Validating PowerPath with the cluster software systems requires extensive knowledge and testing of the cluster software with PowerPath. The 2 key reasons customers invest in clusters is for application availability and system scalability. Most customers can achieve >99.5% uptime when deploying a cluster, as contrasted to a single computer server. PowerPath further adds to application uptime by greatly reducing the likelihood of a server failover due to a path failure.

22 PowerPath Foundations, 19 Management PowerPath provides GUI and CLI interface for online management Performance and status monitoring Configuration Channel director and path maintenance Restoring path after repair Testing 2004 EMC Corporation. All rights reserved. 19 When PowerPath is installed, maintenance, configuration and tuning can be performed online without interrupting the applications. When a path failure occurs, PowerPath disables the path. When the user has made a repair, a simple command line entry will enable I/O through the path. The applications will not be affected when re-establishing the path. All components in a Symmetrix are hot pluggable; however, the server does not handle the removal of a cable and channel director. Because the application has only one path to the device, the application will cease functioning. Further more, the server may have to be rebooted to re-establish communication on the channel. With PowerPath, the user can disable a channel causing I/O to use the remaining channels. The user can perform maintenance on the channel director without taking the application down, then, using PowerPath, re-establish the channel. Now every component of the Symmetrix is not only hot pluggable, it is hot serviceable. PowerPath provides tools to look at the behavior of the SCSI I/Os. You can monitor the amount of traffic on each queue and to each device. When PowerPath is installed, all configuration and maintenance is performed online, keeping the server available to do productive, revenue-generating work. PowerPath does not automatically reconnect because: When a channel has failed, you do not want to spend resources checking on it repeatedly If a channel is flaky, you do not want to continue to try to use it while getting intermittent errors and forcing retries across other channels When a channel is lost, the server will continue to operate in a degraded state. How degraded it really is can be easily determined. Take a channel offline. If it causes a serious problem, you can return it to service in a few seconds. Additionally, suppose you have run out of slots on the Symmetrix; you want to add SRDF for disaster recovery and you need to add Remote Link Adapters (RLDs). You can see how the server will respond to having fewer SCSI channels available.

23 PowerPath Foundations, 20 Course Summary Key points covered in this course: PowerPath is server based software that provides multiple paths between the host bus adapter and the Storage Subsystem Redundant paths eliminates host adapter, cable connection, and channel adapters as single points of failures and increase availability Improves performances by dynamically balancing workload across all available paths Application transparent Close integration with most UNIX and NT hosts Supported SCSI, Fibre Channel, and clustered environments GUI and CLI interface for management functions 2004 EMC Corporation. All rights reserved. 20 Thanks for your attention. This ends our training on PowerPath Foundations.

24 PowerPath Foundations, 21 Closing Slide 2004 EMC Corporation. All rights reserved. 21