You have disadvantages and advantages with each approach; it depends on why you’re using RAID. Most people use it for availability. They don’t want a drive to die and end up having to take their system or server down. In that, you don’t use RAID 5. I learned it the hard way and hammer this point home with every RAID-related question I get into on SF.

Why? Because as drives are getting larger, there’s more tolerance for URE, unrecoverable read errors. We had it happen and it isn’t what you want to discover in the middle of a rebuild. Scenario: RAID system with 3 drives. We got an alarm on our Dell with a hardware PERC card that drive C died. Order new drive, swap it out, no problem. In the middle of the rebuild, it died.

According to the diagnostics, there was a “bad spot” on drive B. The system had a silently failed on that drive repeatedly, and now that it was rebuilding the data, it couldn’t read that spot, and no matter how many times we ran the repair even off the controller directly and it each time said everything was fixed, it wouldn’t rebuild. So we have one dead drive and one drive that couldn’t read from a spot…we end up replacing 2 drives and restoring from backup.

Lesson: RAID isn’t a backup, and RAID 5 is no longer an availability option for larger drives.

If you’re looking to increase speed or increase storage sizes, then you can balance that into your decision. You need to define your needs in terms of your needs and goals, not in terms of “I need RAID, which do I use?”

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