Re:The Battle Agaist Any Raid Five initiative (2016)
by skywhopper on Friday July 13, 2018 @03:54AM
(#17521200)
Where is the 2016 from? This looks like it’s from 2003, when RAID levels were something you had to think hard about. I agree RAID5 is unsuitable for most database uses... but I also haven’t had to think much about it in years. RAID5 was all about maximizing drive space while maintaining some level of reliability. It came at the cost of write speed but for many use cases was the ideal mix. For write intensive applications, RAID10 or equivalent across several pairs of disks is a no brainer. But these days in the cloud the physical disk arrangement is not something I spend much time worrying about.
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Re:The Battle Agaist Any Raid Five initiative (2016)
by zeta0134 on Friday July 13, 2018 @04:45AM
(#17521416)
I learned that RAID5 has a hidden gotcha in it's implementation: it maintains just one parity drive, no matter how big the array is. This is a bit counter intuitive; you might expect it to instead maintain 1/3 of the available drive space in parity. I found this out when I ran across a customer maintaining a 23-member RAID5 array. It had tons of usable space of course, but could only tolerate a single disk failure, and worse, rebuilding that disk required fully reading all 22 remaining drives to recalculate parity across the whole set. Somehow it hadn't caught fire yet when we discovered it, but it was a disaster waiting to happen.
Re:The Battle Agaist Any Raid Five initiative (2016)
by korinthian on Friday July 13, 2018 @05:12AM
(#17521513)
> just one parity drive
That's not RAID5, that's RAID4.
Re:The Battle Agaist Any Raid Five initiative (2016)
by krylon on Friday July 13, 2018 @05:40AM
(#17521609)
Technically true, but with RAID5, you still only get one drive's worth of redundancy, no matter how many drives are in the array.