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Comment by tux3 | Hacker News Reader

RAID or not, if you lose an active drive you will need to 1) restore from backup, 2) fill a new backup drive

If it takes days to fill your new 50 TB backup drive, you have the same problem RAID5 has with rebuild times. The drive might fail in the middle.

RAID isn't a backup mostly because if you overwrite RAID data, you wrote over every copy at once. Non RAID offsite backups don't solve any problem related to drive size, they just make it a lot less likely for a single event to take everything out in the same minute.

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> RAID or not, if you lose an active drive you will need to 1) restore from backup

Er what? I've had production machines lose a drive, have it replaced, and never leave production. Why would you need to restore from backups?

Right, that was said very poorly. What I really wanted to express was that you need to fill a new drive either way, either by resilver or by making a new backup. Point one is bad, not sure why I wrote that!

Absolutely, you want RAID + backup, not one or the other.

50TB at 200MB/s is about 72h. Doesn't seem to be a particularly problematic rebuild time (and that's assuming 100% filled). Of course you need to do regular data scrubbing. If your rebuild is the first time the data is being read in 5y, that might not go so well.

> 50TB at 200MB/s is about 72h.

Assuming the device is offline for users during that time, otherwise there may be reduced throughput.

Yes, and this can be quite painful.

If you have standby sets (like a read replica of a db that can take over for master, or a DR site), you can switch temporarily.

It’s good to know what throughput you have under load for this reason among others.

Also, you can slow or pause some RAID during peak hours.

But if we are talking about a NAS, hopefully you also have SSD caching which should reduce a lot the workload on your disks.

> RAID or not, if you lose an active drive you will need to 1) restore from backup

RAID 1 joins the chat

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