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Re: Sizing - RAC, storage subsystem EMC

From: Binley Lim <>
Date: Thu, 22 May 2003 12:42:59 -0800
Message-ID: <>

This message refers to SAN, but NetApps are happy to recommend a large number (>10) for their RAID-4 NAS as well.

The NAS vendor say you can "carry on" during the resync, but I suspect very few souls will do this if they can help it. If you choose to "carry on", detection of any potential failure of a second disk "will stop the storage server".

As an optimist, I would like to believe the storage vendors can get things right. I would rather not spend time on I/O distribution across individual mountpoints/spindles/small-volumes. Let the storage vendors take care of such details.

  Oh man, .One parity disk for 10-20 disks means that if *any* single disk in the group fails (which will happen five times more frequently in a 20-drive group than in a 4-drive group), then for the duration of the partial outage every single read from the failed disk is going to engage all 10-20 disks in the group. And the resynchronization of the new disk, once it's plugged in, is going to require the *full disk scan of all 10-20 devices*. I wouldn't want to be anywhere nearby when *that* happened.    

  Cary Millsap
  Hotsos Enterprises, Ltd.


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Author: Binley Lim

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