3 posts • joined 9 Dec 2010
How the hell this would work in a shared storage cluster environment? I can't imagine it would be remotely possible.
I can see the fail now:
"We took a RAC cluster and unbeknownst to the DBAs, the server guys replaced the HBA with Folgers Crystals (errr QLogic Flash-Cache HBAs) and then suddenly massive data corruption ensued."
Mmmmmm MS Exchange .... STILL powered by JET "database" technology. I'm still floored that the whole IT industry continues to apply workaround after workaround for this horrendously engineered product. Yes I know the functionality is there and everyone is used to Outlook (for better or worse), but damn the underlying datastore is a house of cards. MS could learn a few things from SQL Server at the very least!
Scrub it... regularly
Yup RAID6 or mirrors are smart, but there is one thing to remember - especially with using larger capacity or SATA drives in any RAID: DO regular routine parity / mirror block checks!
One of the (behind the scenes) features you see in the enterprise arrays (and Linux software arrays from the major distros nowadays) is a background parity raid scrubbing feature or at least a periodic scan during off hours. Extra parity bits (RAID6) or mirrors are definitely a good thing - but there is absolutely no replacement for occasional background reading of all blocks on your arrays. I can't begin to explain the number of times I've seen small raid rebuilds "fail" due to a bad block that accumulated over time but wasn't scrubbed when there was another disk to rebuild from. Data can be corrupted due to noise / vibration / or just bad luck. You don't want to find out about parity block 45698 being bad when the rebuild kicks off due to a real disk kicking the can.
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