Risks when expanding RAID5?

Hello,

maybe you contribute to this thread by describing experiences you've made (or want to avoid) when expanding a RAID5.

Thinking about risks expanding a RAID5, the following dangers come to my mind:

RAID5 is your data's lifesaver when one hdd becomes defective.
=> When adding more than one hdd to an existing RAID5 at a time there is a higher risk while reshaping (adding the new hdd's to the RAID5). This can be avoided just adding one hdd at a time.
Disadvantage of this process is the time needed for reshaping. This time is nearly equal to adding x hdds at a time. For example adding one 4TB hdd to my RAID5 (4x4TB) takes approx. 24 hours, adding two 4TB hdds at a time takes 24 hours too.

Please correct me if I'm wrong and any addition is welcome.

Kind regards tsch

Thanks for your reply.

I can understand your point of view but for me the "anachronistic" RAID5 is far better/safer than using JBOD's and fits my needs concerning safety. The failure of one hdd is much probable than two ore more hdd's failing at the same time.

An yes, you're absolutely right, RAID is no Backup. But I personally don't need to backup everything saved on my NAS.

It was not my goal to start a discussion "RAID vs Backup" in this thread.

Zitat von ryecoaaron

I would never add two disks to a software raid 5 array at the same time.

We bring that up so that other people reading this thread don't think RAID is backup or really a safe option (I've seen too many unrecoverable arrays)...

Thanks for your confirmation regarding 1 hdd vs 2 hdds at the same time.

You and tkaiser are right to mention that RAID5 is not a backup. I had a lot of discussions in my organisation why to spent a lot of money for a professional backup-solution since we have a SAN in two datacenters with syncronous mirroring (and internal RAID).