The HP XP256

The mainframe storage vendors took advantage of the storage consolidation momentum by providing new subsystems that enable the attachment by both open and mainframe servers. However, the traditional open systems storage suppliers mostly choose to ignore the consolidation opportunity and the data warehouse requirements. One exception is HP.

The mainframe storage vendors were all quick to take advantage of the storage consolidation momentum current in the IT industry. They provided new subsystems, or enhancements to existing subsystems, enabling attachment by both open and mainframe servers. A variety of subsystem resident software added value in the areas of copying, moving and backing up of data. These subsystems are referred to as Multi-Platform Storage Subsystems. These products also found value to IT organizations planning Data Warehouses. Data Warehousing typically gets the majority of data from MVS systems, but invariably runs on a non-MVS platform. Moving data from MVS to an open server quickly and efficiently, without using LANs, WANs or bulk tape, is a real advantage of multi-platform products.

Despite these benefits, the traditional open systems storage suppliers mostly chose to ignore the consolidation opportunity and the data warehouse requirements. One exception is HP. HP had a marketing agreement with EMC enabling them to sell the EMC 3000 product on HP servers.

HP became aware of the need for a multi-platform product and were also concerned that EMC systems and their SANs strategy could lock in customers to a single storage vendor. HP needed a product that matched or exceeded the attachment flexibility, performance and scalability of the EMC products. They also needed MVS skills to go along with this multi-platform product. In May 1999, HP announced a Joint Technology (JTA) and OEM agreement with Hitachi Ltd. and Hitachi Data Systems (HDS).

Under the terms of the JTA, the research and development organizations of HP and Hitachi Ltd., in conjunction with HDS, will cooperate on the design, development and enhancement of enterprise-storage products. The initial result of this agreement is the Multi-Platform HP SureStore E Disk Array XP256, which with the exception of the disk devices, has a basic architecture similar to that of the HDS 7700E.

Under the terms of the three-year OEM agreement, HP will market Hitachi’s high-end array technology products.

HP will also OEM several storage management software features, similar to those of the 7700E offerings, and integrate them into its new SureStore E Storage Node Manager, as well as OpenView OmniBack II to support SAP and Oracle applications. HDS, for its part is now an authorized value-added reseller for the XP256.


Open systems support includes the HP-MPE IX, HP-UX, IBM AIX, Linux, Sequent Dynix, SGI, Sun Solaris and multi-vendor Windows NT platforms and support for MVS. Host attachment is provided by Fibre Channel, SCSI-2, Ultra SCSI, OEMI and ESCON with a maximum of 32 concurrent I/O operations. Scalable capacity ranges from 60GB to 9TB using a combination of 2.5 inch 12,030 RPM 15GB disk devices or 3.5 inch 6,300 RPM 36GB disk devices. Both RAID-1 and RAID-5 are supported with the ability to intermix RAID levels. As with mainframe subsystems, there is remote "phone home" capabilities and the fault-tolerant, redundant architecture has no single point-of-failure, which includes a 16GB mirrored cache.

The system comes with full software and solution integration with XP/ServiceGuard and MetroCluster and with support for ContinentalClusters available at a later date. HP maintains a 99.999 percent uptime guarantee with HP’s Mission Critical Server Suites. The XP256 is described as "SAN ready" with support for the HP SureStore E Switch F16, Hub S10 and Hub L10.

As with the HDS 7700E, an XP256 subsystem consists of one Control Frame and from one to four Array Frames. The Control Frame contains the Channel Host Interface Processors (CHIPs), Array Control Processors (ACPs), nonvolatile cache, and Control Store Logic. The XP256 has up to 16GB of cache, up to four pairs of CHIPs, and up to four pairs of ACPs supporting one or more arrays of 15GB, and/or 36GB SCSI disk devices. Up to eight dynamic spare disk devices can be included, with one per disk device type installed as a standard feature.

The Array Frames contain the disk devices. The XP256 can contain up to 256 15GB and/or 36GB disk devices. The device specifications are different from those offered by HDS in the 7700E.

Capacity will vary depending upon the types of disk devices installed, number of logical volume images, RAID levels, disk emulation modes and LUN sizes, and number of ACP pairs. Connectivity will vary upon the number and type(s) of CHIPs. Performance will vary depending upon the amount of cache, types of disk devices, number of CHIPs and ACPs. As with all multi-platform products, determining the potential configuration options is complex. HDS has a configuration program that will validate configurations based upon a variety of "intermix rules" and we assume a variation of this program is available for the XP256.


CHIPs provide the host interface on the XP256 subsystem. They process commands from the host and manage accesses to the cache. Each CHIP is a single card (printed circuit board) containing four Intel i960 66MHz microprocessors. The CHIP cards are always installed in pairs for redundancy, with a maximum of four pairs per subsystem. The CHIPs in the XP256 contain four active Intel i960 66MHz microprocessors per CHIP board enabling up to four concurrent transfers per CHIP.


ACPs are the equivalent of a disk director, and are only available in pairs. Each ACP is a single card (printed circuit board) containing two microprocessors. The ACP also controls data movement between the ACP buffer and the SCSI disk devices. The microprocessors in the ACP initiate the data movement to/from the disk devices, and then Direct Memory Access (DMAs) in the SCSI path interface controllers continue the transfers, freeing the ACP microprocessor to perform other operations.

The XP256 supports one, two, three or four pairs of ACPs. Each ACP has two active Intel i960 66MHz microprocessors per board, four 20MB per second SCSI interfaces per board and two SCSI paths sharing a microprocessor and parity circuits.

ACPs are also responsible for parity generation. They perform the function of rebuilding data from existing data and parity in the event of an HDD failure in the RAID-5 architecture. In the RAID-1 implementation, the ACPs control copying data from the good HDD to a dynamic spare in the event of an HDD failure. The ACPs also perform the function of copying the data to a replaced HDD in an Array Group from the spare or performing a Construction Copy process to a replaced HDD in RAID-5 if for some reason a spare was not used before a failed HDD was replaced.


In the logical diagram it may seem like the CHIPs and ACPs can transfer data directly via the bus. However this is not the case. All data must be transferred into and out of the cache, to and/or from the host or SCSI disk devices by use of the multiple data buses.

Each CHIP and each ACP is attached to the two 252MB per second data buses and the two 120MB per second command buses. The two data buses function together as one 504MB per second data bus. Each CHIP or CHIP pair, and/or each ACP or ACP pair may be accessing both data buses simultaneously to achieve an instantaneous data rate of 504MB per second. The data buses are First Come First Serve (FCFS) priority arbitration and are non-preemptive and non-interleaved. When data is placed on the bus each packet is addressed and time stamped so that the appropriate CHIP pair, ACP pair, or cache will receive all the data between time stamps. Hitachi Data Systems states that the philosophy of the multiple bus design is that by utilizing the 504MB per second instantaneous data rate capability, the CHIPs and ACPs are able to transfer data to and from cache faster than the host interface paths or back-end SCSI paths can fill the buffers allocated to those paths.

The XP256 has two 120MB per second command buses thereby eliminating bus contention between I/O commands and large data transfers that can occur on shared busses. Each CHIP and ACP has a high speed command buffer to use as a scratch pad.

There is also a Hot Line bus that is used during diagnostic and error recovery procedures for the microprocessors. The purpose of having this separate bus is to eliminate any possibility of command or data bus failure due to microprocessor failures.


The software-based features of the XP256 are as follows. Where applicable, the equivalent HDS 7700E and EMC Symmetrix offerings are provided in parenthesis ( / ).

• HP SureStore E Business Copy XP (ShadowImage/TimeFinder): Creates copies of volumes on the same XP256 subsystem.

• HP SureStore E Continuous Access XP (HRC/SRDF): Creates mirrored copies of volumes on another XP256 (local or remote).

• HP SureStore E Data Exchange XP (HMDE/InfoMover): Provides high-speed transfer of data between HP-UX and mainframes using channel resources.

• HP SureStore E Secure Manager XP (not available/Volume Logix): Secures data between servers when multiple servers access the same subsystem via a SAN.

• HP SureStore E LUN Configuration Manager XP (LUN Manager/Symmetrix Manager): Enables LUN configuration.

• HP SureStore E RAID Manager XP (not available/Symmetrix Manager): Provides server-based software to manage Business Copy XP and Continuous Access XP.

• HP SureStore E Remote Control XP (not available/Symmetrix Manager): Provides remote Web-based configuration and system optimization.

• HP SureStore E Cache LUN XP (FlashAccess/PermaCache): Locks user-definable data into cache.

• HP SureStore E Performance Manager XP (GraphTrack/Symmetrix Manager): A graphical, Web-based tool to monitor performance, provide notification of degradation, and adjust storage-tuning parameters.

• HP SureStore E Resource Manager XP (HMRS/ESP): Allows sharing of XP256 resources between mainframe and open systems platforms.

• HP SureStore E Continuous Track Manager XP (Hi-Track/Phone Home): Monitors systems status, reports errors and failures via phone home capabilities.

Cementing its commitment to the XP256, in December 1999, HP announced a complete integrated solution for NT consolidation, its "Stress-Free NT Storage Consolidation." The NT consolidation package provides for the connection of hundreds of NT hosts (Compaq, Dell, HP, IBM), centralized management, and security.

The NT consolidation solution features several new HP software products and new features for the XP256:

• HP SureStore E SAN Manager LM (LUN Management): Provides host-level security and the management of logical devices.

• HP SureStore E Secure Manager XP: Protects from the possibility of a rogue-sever accessing storage.

• HP SureStore E Auto Path XP: Provides automatic path failover and load balancing for NT servers.


The XP256 is just one piece of HP’s storage strategy. Although HP stated that they would continue to resell EMC’s Symmetrix products, the message is clear that the XP256 is their preferred offering.

As with any OEM agreement where two vendors are marketing basically the same product, the potential exists for "channel conflict." Evaluator Group believes that this issue has been addressed between HDS (a certified XP256 reseller) and HP.

The ITcustomer community will receive benefits in the area of increased feature/function and lower prices as the enterprise storage market becomes more competitive.

– Dick Bannister is a Senior Partner at the Evaluator Group Inc., an industry analyst organization focused upon storage products.He can be reached at (303) 221-7867, or via e-mail at