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Re: what to get with 20K

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Bob ZelinRe: what to get with 20K
by on Jan 9, 2011 at 4:27:30 pm

Eric Cox writes -
Don't do RAID 5 on multi-terabyte volumes


Eric,
where do you get this nonsense from? RAID 6 makes sense only for drive arrays with 16 or more drives. A typical small user will buy an 8 bay array, because they want to save money. An 8TB array becomes 6.5TB after RAID 5, and the performance slows down from RAID 0. Now, make that RAID 6, and you get even LESS storage and less performance (throughput) - yes, you have your protection, but at what cost to the user.

Most manufacturers preconfigure their arrays (even 16 bay arrays) to RAID 5 from the factory (think Sonnet, Active Storage, Cal Digit, JMR, Maxx Digital, Small Tree, etc.). RAID 6 is a great idea if you have no one there to ever administrate the system, but again, you lose performance, and total available size of the array.

So, what is the best "modern" configuration (which will be outdated in 3 months) - the configuration that JMR uses - a split buss 16 bay chassis, split into two 8 buss groups, each with their own SAS host adaptor card SET UP FOR RAID 5, stripped into a RAID50 config. This is how you get 1200MB/sec - enough for your uncompressed 4K work. But once 6 Gig drives with 6 gig host adaptors and 6 gig backplanes become commonplace (sometime in 2011), then EVERYONE will be getting close to 2000MB/sec, and all of this will be moot.

Everyone is a big shot on these forums, but the reality is that most people (most clients) have NO MONEY, and are trying to do things as cheaply as possible - (read: the most storage for the least amount of money, with the best performance) - and NO ONE that I know would accept an 8 bay chassis configured in RAID 6, no matter how "safe" it was.

And even with RAID 6 - if you don't occationally check your server, to see if you have a failed drive (don't even start with me about you should have the host adaptor email your SMTP mail server with the failure notice - what planet do you live on ?) - then even with RAID 6 and a hot spare ready to go (in your 8 bay), then you will STILL lose all your data, because if you are lazy, and never bother to look, then THREE drives will fail, and you are still screwed.

I just had a client lose all his data on an 8 bay - he saw the RED light flashing on the array, and the ATTO SAS EVEN HAS OCCURED - DRIVE 2 HAS FAILED - but did NOTHING ABOUT IT (what is your explanation about that Eric ? ) - and then had ANOTHER DRIVE FAIL (it was RAID5), so they lost all their data, and only called after the second drive failed. Didnt' they notice the red flashing light on the array, indicating a failure - dont' you think they might have called me to ask "gee, what's that red light mean" (yes, they were trained on all of this 2 years ago) -

Don't live in fantasy land. If you do this for a living, you know exactly how clients behave, and what they expect. And professionalism is not one of them.

Bob Zelin



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