Monday, 23 March 2009

On Board RAID vs. Add-In RAID Controller and Drive Failure Behaviours

When it comes to balancing the abilities of a server versus its cost, one of the first things to go is the add-in RAID controller.

When it comes to the upfront cost for the add-in RAID controller, it is virtually paid for in improved performance.

The catch with that though is when the first drive failure happens. While not common, drives are mechanical in nature and do fail over time.

The behaviour we have seen on an array member failure when connected to the on board RAID is a server lock-up. Now, for SBS, we can catch it pretty quick when we do not receive a report on the server in the morning, or via phone call if the failure happens during the business day.

There is also the additional cost of having us come down in emergency mode to make sure everything comes back up okay if there was a lock-up.

The add-in RAID controller on the other hand does not flinch. It has the ability to work with an array member failure and transitions the array state accordingly without impact to the server.

While some of the newer on board RAID controllers have the ability to do hot spares, the rebuild of the hot spare into an existing array with a failed member will directly impact the server’s performance.

A hot spare that is dropped into a failed array member’s spot on an add-in RAID controller will not impact the server’s performance for the most part.

As a result of some of the drive failure situations that we have seen, we no longer forgo the add-in RAID controller in any of our client’s sites. It does not pay in the long run.

Philip Elder
Microsoft Small Business Specialists
Co-Author: SBS 2008 Blueprint Book

*All Mac on SBS posts will not be written on a Mac until we replace our now missing iMac! (previous blog post)

Windows Live Writer

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