Back at SFD10 a couple of weeks back now when visiting with Nimble Storage they mentioned that their latest all flash storage array was going to support triple-parity RAID.

And last week at a NetApp-SolidFire analyst event, someone mentioned that the new ONTAP 9 triple parity RAID-TEC™ for larger SSDs. Also heard at the meeting was that a 15.3TB SSD would take on the order of 12 hours to rebuild.

Need for better protection

When Nimble discussed the need for triple parity RAID they mentioned the report from Google I talked about recently (see my Surprises from 4 years of SSD experience at Google post). In that post, the main surprise was the amount of read errors they had seen from the SSDs they deployed throughout their data center.

I think the need for triple-parity RAID and larger (+15TB SSDs) will become more common over time. There’s no reason to think that the SSD vendors will stop at 15TB. And if it takes 12 hours to rebuild a 15TB one, I think it’s probably something like  ~30 hours to rebuild a 30TB one, which is just a generation or two away.

A read error on one SSD in a RAID group during an SSD rebuild can be masked by having dual parity. A read error on two SSDs can only be masked by having triple parity RAID.
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