Section 9.5. Practical Implications | Inside Windows Storage: Server Storage Technologies for Windows 2000, Windows Server 2003 and Beyond

9.5 Practical Implications

RAID presents an attractive solution for ensuring performance and high availability. Several RAID schemes have been designed to meet a variety of needs. For the Windows NT platform, software RAID solutions are available. In particular, Windows 2000 and Windows Server 2003 ship with the Logical Disk Manager driver that implements software RAID solutions. Software RAID solutions can consume a measurable amount of CPU cycles because each I/O needs to be translated twice. The first translation is performed within the file system from a file-relative offset to a volume-relative offset. The next I/O is performed within a software RAID solution ( assuming it is deployed for the I/O of interest), where the I/O is translated from a volume-relative offset to a disk-relative offset.

Microsoft has made available to vendors an MPIO development kit for building a high-availability and high-performance multipath I/O solution. Customers need to get the solution from vendors and not directly from Microsoft. The MPIO kit allows for compliant solutions from multiple vendors to coexist on the same Windows server. This is unlike the solutions previously available from vendors, in which the vendor solutions did not interoperate . It appears that there will be downward pricing pressure in this area of the market. Furthermore, solutions built on the Microsoft MPIO kit will not require customers to lock in to only one vendor, because different vendor solutions can now coexist. Storage solution procurement officials should bear this in mind when talking to their vendors . It is also worth watching whether Microsoft introduces some kind of logo scheme for such solutions and how rigorous the testing requirements are to achieve that logo.

Several vendors have also designed software mirroring and replication schemes. While considering such software, procurement officials should also keep in mind the new volume shadow copy architecture described in Chapter 5, which could be a better alternative for their needs.

This segment of the market also bears watching with the advent of IP storage because it is very likely that some vendors will build similar solutions using iSCSI.

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