Difference between Raid 5 + Global Spare or Raid 6

  • Last Post 11 January 2019
Marcel Claus posted this 08 January 2019

I own a Pegasus2 R6. I've replaced my original disks with 6 new ones, so I need to need to build a new array and logical drive. I prefer to choose for a raid level that will give me maximum protection. The Pegaus2 manual points out that Raid 6 is the safest Raid level. 

Now I'm wondering if there is a difference between choosing Raid 6 (using all 6 disks) or choosing Raid 5 with a global spare configured (so 5 disks in Raid 5 and 1 for the spare). Since Raid 5 performs slightly better then Raid 6, would this give me the same safety net as Raid 6 when 2 disks fail but with better performance?

Thank you for your advice!

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Raghuraman Kannan posted this 10 January 2019

Hi Marcel,

As you have mentioned, RAID 5 has better Performance compared to RAID 6.

So , it would be better if you go for RAID 5 and an Global spare than RAID 6.

Thanks !

PROMISE Technology Inc. posted this 11 January 2019

Hi Marcel,

I prefer to choose for a raid level that will give me maximum protection. 

If you want maximum protection you should go with RAID6. With RAID6, any two drives can fail and your volume will stay online. With RAID5, if one drive fails, then a rebuild will start on the global spare, if another drive fails during the rebuild, you are then 2 drives down on a RAID5, which is a bad thing.

With todays large drives, rebuilds can take a long time. There was a study done by a large datacenter a few years back and perhaps one of the most interesting conclusions was that when one drive in an array fails, another drive is ready to fail. And I have seen cases where a 2nd drive in a RAID6 failed while a rebuild was in progress. Since it was RAID6 everything was fine.

If performance is the requirement, RAID5 is the way to go. If data security is the issue, RAID6 is the way to go.