Forget what you might have heard about host-based volume managers. Here are seven reasons why they deserve some respect.
Host-based volume managers (also known as logical volume managers or LVMs) are the most underrated or underutilized components in storage ecosystems, even though they've been around almost as long as open systems. Perhaps because they're host based or often managed by sys admins, many storage administrators don't consider LVMs part of their toolset. I'll set the record straight regarding LVMs and, hopefully, encourage storage administrators to use them to improve the performance of their storage environment.
MYTH 1: LVMs aren't required for good performance or balance.
Technically, volume managers aren't necessary for hosts such as Fibre Channel, iSCSI, parallel SCSI, JBOD or hardware RAID to access storage. To some extent, storage (hardware) vendors have made matters worse by creating a general dislike for the use of any host-based utilities that duplicate functions in their arrays, primarily RAID.
However, as the source of all IO, a host has a lot of control over how IO is distributed along the path and its final destination (the array itself). LVMs let you control and distribute this IO without putting the entire onus on the array, which may not be sufficient.
Most LVMs work by introducing a logical layer between the IO access methods (such as file systems) and the physical
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access layer (such as device drivers). This logical layer is capable of performing multiple functions such as software RAID, which, when used with device-access mechanisms, allows IO to be spread uniformly across "egress" paths such as host bus adapters (HBAs). This way, when the host gets busy, the array doesn't see all of the access coming in--or headed to--a single location, keeping its own IO subsystem balanced.
This was first published in October 2007