Modular arrays earn new trust


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How a monolithic array may price out

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$450,000: HDS' 9970V includes hardware features of 3TB of raw storage, FC HDDs, two controllers, eight FC host ports, 8GB cache and RAID 1 and 5. Software features such as LUN masking and array management with remote copy, D-2-D backup and snapshot may cost extra.
$750,000: HDS' 9980V include hardware features of 6TB of raw storage, FC HDDs, four controllers, 16 FC host ports, 12GB cache and RAID 1and 5. Software features such as LUN masking, array management with remote copy, D-2-D backup and snapshot may cost extra.
$2,000,000: HDS' 9980V include hardware features of 18TB of raw storage, FC HDDs, four controllers, 16 FC and 16 ESCON host ports, 32GB cache and RAID 1 and 5. Software features such as LUN masking array management with remote copy, D-2-D backup and snapshot may cost extra.

Modular management
Users familiar with managing monolithic arrays will be pleasantly surprised by the management software for modular arrays. Older monolithic arrays such as HDS' 7700Es or EMC's Symmetrix 8830s required users to gain a fair amount of expertise on the storage array and have an in-depth knowledge of the array's applications. Even then, some configuration changes such as moving LUNs from one port to another or reformatting disk drives on the array required a trained engineer. That engineer was often a vendor employee .

With older monolithic arrays, LUNs have to be carefully chosen and assigned to the application. If you place too many LUNs behind a single controller for a performance intensive application, applications may experience bottlenecks and degraded performance.

Before the advent of modern modular arrays, to proactively prevent bad performance, storage administrators needed to spend a fair amount of time understanding the application and carefully manage how the data on the LUNs got distributed throughout the storage array. This became more art than science because the administrator had to be expert in both the application and in the layout and management of the array.

Today's modular storage arrays go a long way in eliminating both problems. The new software removes the need for a vendor engineer any time a LUN needs to be moved from one FC port to another. Rather than writing special scripts or purchasing additional software to enable this task, some current management software makes this a point and click operation.

The software allows users to visualize which LUNs should be assigned to which FC ports. The software automates the actual assignment. While that doesn't prevent administrators from taking away LUNs already assigned to applications, it reduces the amount of time and technical expertise required to administer the storage array. For instance, EMC's Navisphere Manager--used to manage Clariion arrays--provides users with a browser based interface, permits administrators to create RAID groups automatically or manually and then allows LUNs to be created from these RAID groups.

It's also more difficult with monolithic arrays to place and move LUNs on the FC ports. Originally designed to support the mainframe environment, monolithic array LUNs usually get configured during installation and setup, and then are presented on individual storage array ports for use by the mainframe operating system.

This design strategy doesn't work in today's networked storage environments. Different servers with different operating systems may connect to the same storage array. In certain environments, servers with different operating systems access different LUNs on the same storage array FC port. Users of some monolithic storage arrays still need to verify with their storage vendor that a Novell, a Window and a Unix server may concurrently access different LUNs on the same FC port.

Some modular arrays address this unpleasant reality. The software on their arrays recognizes that even though most operating systems use SCSI to talk to disk drives, each OS has its own nuances in terms of how it talks to the disk. Most vendors now recognize this and have included code in the latest microcode levels on their storage arrays to address most if not all of these concerns. Vendors such as 3PAR, EMC, HDS, Hewlett-Packard Co. (HP), IBM, nStor and others now claim interoperability with all current, major releases of Unix and Windows operating systems for their storage arrays. However, users should still be cautious about presenting LUNs on the same FC port to multiple different operating systems and test that in their own environments.

Modular array features at different price points

This was first published in January 2004

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