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Best Practices: Finding the logic in volume managers

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MYTH 6: LVMs can cause a performance overhead on the host.
Some people may still believe an LVM introduces latency on the host and takes away precious CPU and memory resources that could have been allocated for app performance. Not true. CPU and memory units have become inexpensive and servers more powerful. And improvements in technology have allowed vendors to make LVMs more efficient.

It's important to mention that parity-based RAID levels, such as RAID-5, are still off limits for LVMs. Many vendors have tried to make them efficient, but my preference is to leave those functions to the hardware arrays.

MYTH 7: LVMs can't provide data mobility and protection.
Almost all LVMs these days contain some form of data mobility functionality in addition to core functions such as RAID protection. These features vary depending on the vendor and they're still proprietary. However, most vendors support data migration functions, network-based remote replication for off-host processing or disaster recovery, and snapshots and point-in-time copies for off-host processing and backups.

That said, there may be certain efficiencies in performing these functions within the storage array, but it will come at a cost. Many operating system vendors that provide LVM packages bundle such features or offer them at a fraction of the cost. LVM-based data mobility should therefore be evaluated to see if

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it's a cheaper and more viable option for your requirements. Some LVMs are also now capable of providing clustering support for apps such as Oracle RAC 10g.

The performance of a storage subsystem hinges on how its "customers" (the hosts) access it. An LVM can play the role of traffic cop, and its value should never be underestimated or overlooked.

This was first published in October 2007

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