How VERITAS Volume Manager Complements Hardware RAID in Microsoft Windows Server Environments

Transcription

1 How VERITS Volume Manager Complements Hardware RI in Microsoft Windows Server Environments V E R I T S W H I T E P P E R

2 Table of Contents The usiness Problem High vailability Flexibility in Storage Solutions Implementation ifferences Hardware RI Software RI How Volume Manager s Software RI complements Hardware RI Higher vailability via Extended ata Protection Improved vailability via Flexible RI Configuration and Management etter vailability and Manageability via Larger LUNs Improved vailability via On-disk Configurations Increased Performance via Striping across Multiple rrays etter Manageability via Storage Vendor Independence Summary

3 The usiness Problem High vailability More and more electronic information users today are demanding 24xForever access to data. Especially in expanding e-commerce driven environments, downtime is increasingly not acceptable, because consumers can very quickly jump to a competitor s Web page if yours is not available. Lowering system downtime is now a business necessity. ut doing so is not free. On the contrary, systems solution costs often rise exponentially as more 9s of availability are configured into the system. nice balance of cost versus availability is possible through the careful application of hardware and software solutions in key areas such as system online storage, without the need to spend huge sums of money. Increasingly, storage is a key element in overall system availability. Storage-management techniques can play a crucial role in creating highly available environments based on Microsoft Windows Systems. This paper illustrates some techniques for using VERITS Volume Manager to reduce downtime, increase performance and provide higher availability, all in a costeffective manner. Flexibility in Storage Solutions n important aspect of investment protection in storage purchases is how well the storage system can grow, for both planned and unplanned events. Organizations may wish to spread their risk by not betting on any single storage vendor for all their storage needs. Multisourcing storage systems will help spread this risk. The ability to mix and match storage from multiple vendors and still construct high-performance highly available storage is greatly enabled by competent host-based volume management tools such as VERITS Volume Manager for Windows. However, managing storage from multiple vendors can place a large burden on already overloaded system administrators, because they would need to learn to become proficient with multiple interfaces. In this case as well, by using host-based VERITS Volume Manager, the system administrator will have domainwide Windows storage management from a single GUI console. RI subsystems are great for protecting against disk failure and to improve I/O performance. ut what if (or when) a RI subsystem itself fails? nd, what if you need more I/O performance than the RI subsystem itself can provide? Using hostbased volume management, software RI may be applied across RI subsystems from the same or different vendors, thus aggregating all the desirable properties of RI subsystems. VERITS Volume Manager provides this extra dimension of flexibility to RI subsystems, consequently increasing your overall data availability and I/O performance. Implementation ifferences Hardware RI Hardware RI implementations typically employ RI capabilities via firmware or downloadable software running in the Host us dapter (H) or an array-based controller. ny RI calculations or management overhead are performed in a dedicated processor on the controller or in the H. Controller-based RI can be implemented in three primary flavors: 1. Embedded directly with an H, to which a set of disk drives is connected 2. Via an external storage system containing disk drives and controllers typically housed in a separate box 3. In a storage appliance or file server, where the RI functionality is run on a dedicated processor along with protocolspecific instructions such as CIFS for file sharing How VERITS Volume Manager Complements Hardware RI in Microsoft Windows Server Environments Page 1

4 ecause the host system dispatches logical I/O requests to the controller in a hardware implementation, the reductions in bus traffic and system CPU use can be significant. This is the primary area where hardware RI has the advantage, and it should be exploited. For example, in a hardware controller implementation of mirroring, the host would pass each write through the disk driver and across the I/O bus, where the controller would break it down into two separate writes. In the same mirroring application with host-based RI, the host system CPU would break the write down into two separate disk write operations, using some CPU bandwidth to do so. In addition, two separate write operations would flow across the I/O bus, taking some I/O bus bandwidth. lthough the mirroring example is not very dramatic in terms of additional CPU and I/O requirements for a host-based approach, the picture is more critical for RI-5 configurations. ecause of the complexity of the parity calculations, the CPU requirements on host-based RI-5 can easily reach into the 20 percent range. In addition, the I/O bus bandwidth requirements may be significantly increased as well for host-based deployment of RI-5. Software RI The CPU and I/O bus bandwidth limitations described above for hardware implementations are significant only if the host system is configured so lean as not to have resources available in these two areas. It is, in general, much simpler to add processing power or bus bandwidth at the host system side than in an array subsystem. Host-based RI implementations offer more flexibility in configuring disks because they build RI objects from logical portions of disks. dditionally, because the disks that make up a RI object in a software implementation do not need to be connected to the same controller or H, it is possible to attain increased performance and availability. How Volume Manager s Software RI complements Hardware RI oth hardware and software RI offer benefits. However, by combining VERITS Volume Manager for Windows with RI subsystems, the total solution can attain new levels of availability, flexibility, performance and manageability. This paper presents some examples of these combinations. Higher vailability via Extended ata Protection Most low-end and midrange controller-based RI solutions contain single points of failure in components such as a host connection, channel or power supply. If any one of these components fails, it will take the entire RI subsystem down. y applying host-based software RI techniques across separate hardware RI subsystems, you can protect against many points of failure. VERITS Volume Manager for Windows can be used to mirror selected volumes in separate enclosures. In the event of a channel, host connection or power-supply failure in a single enclosure, data access can continue by using the mirror copy. Thus, administrators can build and implement storage configurations with the availability and reliability characteristics typically found only in high-end arrays, but with much less total capacity used and at a much lower cost. n example of this RI configuration applied to disks or volumes is illustrated in Figure 1. Page 2 How VERITS Volume Manager Complements Hardware RI in Microsoft Windows Server Environments

5 Two Mirror sets created with Volume Manager C C C RI rray Enclosure 1 RI rray Enclosure 2 (with Mirrors) Figure 1: Mirroring with Volume Manager from one RI subsystem to another Improved vailability via Flexible RI Configuration and Management Hardware RI subsystems often need to be tuned for optimal performance after initial setup, once the actual I/O pattern of users is seen. Plus, the I/O pattern may change over time, requiring further tuning. In addition to changes in I/O patterns, changes in user access patterns, read/write ratios and workload transfer sizes will likely occur. These changes will necessitate reconfiguration of RI in the hardware array. With controller-based RI arrays, these changes are usually achieved by first making a backup copy of the data, reconfiguring the array and then reloading the data back onto the array. The downside to this approach is interruption to users data during this process not the optimal situation. The online reconfiguration capabilities of VERITS Volume Manager for Windows will allow users to have uninterrupted access to their data while RI configuration changes are being made. Volume Manager permits online creation and growth of mirrored, striped, RI-5 or mirrored striped volumes. In addition, to eliminate performance bottlenecks, Volume Manager can move a portion of a disk (subdisk, in Volume Manager terminology) with a high I/O activity hot spot to a different location where the I/O activity is less, thus improving data availability. Figure 2 shows a screen shot indicating the hot spot and available subdisks with low I/O. Figure 2: Volume Manager GUI for hot-spot detection and subdisk layout How VERITS Volume Manager Complements Hardware RI in Microsoft Windows Server Environments Page 3

6 etter vailability and Manageability via Larger LUNs For any type of RI used in an array, the size of a database or file system is ultimately limited to the maximum size of a Logical Unit Number (LUN) in the particular hardware array. However, this limitation may be removed with VERITS Volume Manager for Windows. dministrators may combine LUNs from multiple RI controllers with Volume Manger to construct a very large volume capable of holding a very large database or file system, spanning multiple LUNs across controllers. This combined capability can give users better access to their data than if the file system or database is split across multiple LUNs. In addition to offering increased availability, the larger volume offers better convenience for system administration. Managing one large volume in a consistent manner will take less time than managing multiple smaller LUNs, especially if arrays from multiple vendors are used. Figure 3 depicts the use of Volume Manager to combine two RI rrays from different vendors to create a larger single file system or database Volume G in this example. LUN G LUN G Volume G 504 G + = G RI rray Vendor RI rray Vendor Flexible Logical Volume Figure 3: enefit of combining LUNs into larger logical volume Improved vailability via On-disk Configurations isk and LUN RI configuration data within each hardware array is stored in the array itself. The information used to relate the storage to the Windows Operating System objects, including the host adapter connection and the mapping of partitions to databases and file systems, is stored in files on the host system. This arrangement can create a hardship if, for instance, the address at which the LUN is connected to the host changes, and thus applications and system tables will need to be reconfigured to reflect the address change. This sort of situation is not uncommon in a multiple host failover configuration or if an array is moved to a different host adapter or if a different type of controller is added to the system, forcing the Windows Operating System to rename its devices. VERITS Volume Manager for Windows stores its configuration data on each and every drive in the array that has volumes created by Volume Manager. The configuration data includes unique position-independent identifiers, so that when a Volume Manager-enabled disk is moved physically or logically between controller addresses (either planned or unplanned, such as in a failover scenario), the system will know how to remap the logical objects to their new physical addresses. This functionality allows Volume Manager controlled volumes to be continuously available during such changes, without the need to modify database or file-system tables. Page 4 How VERITS Volume Manager Complements Hardware RI in Microsoft Windows Server Environments

7 nother advantage to the Volume Manager approach is the elimination of a hard dependency on the Windows registry for such configuration information. Not having this dependency eliminates the risk of having the registry become corrupted and of access to the entire online storage system being at risk. y redundantly storing the configuration data on each physical drive, volumes being managed by Volume Manager will not have the dependency on the Windows registry that other storage subsystems do. Increased Performance via Striping across Multiple rrays Certain high-bandwidth applications such as audio/ video streaming have data-transfer requirements that surpass the capability of a hardware array controller attached to the host by a single connection. What is needed is a way to aggregate the bandwidth of multiple data buses. This can be achieved by using VERITS Volume Manager for Windows to combine multiple hardware arrays connected to the host via multiple buses in a single large striped volume. y combining hardware and software in this manner, the system will be able to achieve the higher transfer rates demanded by some of today s leading applications. Figure 4 shows how to achieve these higher bandwidths flexibly by using Volume Manager and multiple RI arrays. Host System Stripe Set across Raid rrays 1-3 Stripe Set across Raid rrays 1-3 RI rray 1 RI rray 2 RI rray 3 Figure 4: Using Volume Manager to provide faster I/O across multiple arrays etter Manageability via Storage Vendor Independence Host-based RI solutions such as VERITS Volume Manager for Windows simply see storage attached to the host systems as LUNs. LUN is typically associated with a disk drive, but does not in all cases have to be limited to a single drive. What is important is that host-based volume-management software does not need to distinguish if each LUN presented is from different storage arrays, such as from Compaq, ell, EMC, HP, Hitachi, IM or other vendors. Thus, volumes can be created that span LUNs from different vendors, which allows arrays from different vendors to be used together. Volumes can also span LUNs from the same hardware vendor, which can be significant when the maximum LUN limit is reached in any particular RI subsystem. How VERITS Volume Manager Complements Hardware RI in Microsoft Windows Server Environments Page 5

8 Multiple-LUN volumes created with VERITS Volume Manager for Windows can then have RI applied in configurations such as Striped Sets (RI-0), Mirrored Sets (RI-1), Striped Parity Sets (RI-5) or Mirrored Stripe sets. In the case of Striped Sets, the best use of storage will be obtained by using like devices to construct the stripe across. y using Volume Manager to construct any of these RI types across arrays from different vendors, a consistent user interface is applied, saving system administrators time and headaches. Figure 5 illustrates how Stripe Sets and Mirror Sets can be created with Volume Manager across hardware arrays, which can be from either the same or different vendors. Especially when the arrays are from different vendors, these software RI sets will be managed very efficiently from the single Volume Manager console, an advantage over separate consoles from each array vendor. LUN LUN Mirrors of + Stripe Set across Raid rrays 1-3 C C C C C C RI rray Vendor 1 RI rray Vendor 2 RI rray Vendor 3 Figure 5: pplying host-based RI across different arrays using Volume Manager Page 6 How VERITS Volume Manager Complements Hardware RI in Microsoft Windows Server Environments

9 Summary Hardware RI and Software (host-based) RI can complement each other in a variety of configurations to extend the availability, manageability and performance of a storage system. When using a host-based storage virtualization product such as VERITS Volume Manager for Windows to provide the Software RI component, these benefits will contribute substantially toward providing total system availability in the four or five Nines range (99.99 percent to percent), as well as greatly simplifying the system administration of complex storage environments and providing the performance users will expect. How VERITS Volume Manager Complements Hardware RI in Microsoft Windows Server Environments Page 7

10 VERITS Software Corporation Corporate Headquarters 350 Ellis Street Mountain View, C or For additional information about VERITS, its products, or the location of an office near you, please call our corporate headquarters or visit our Web site at V E R I T S W H I T E P P E R Copyright 2001 VERITS Software Corporation. ll Rights Reserved. VERITS, VERITS SOFTWRE, the VERITS logo, usiness Without Interruption, VERITS The ata vailability Company, and VERITS Volume Manager are trademarks or registered trademarks of VERITS Software Corporation in the U.S. and/or other countries. Other product names mentioned herein may be trademarks or registered trademarks of their respective companies. Specifications and product offerings subject to change without notice. Printed in US. May VER06-VMRIWPR