3 NVME Drive RAID

[Raymond Gradzewicz]

Can you create a raid array with two 2TB drives and one 4TB drive, so that the 4TB drive acts as parity for both of the two 2TB drives? So that if one of the 2TB drives fail I can just buy another 2TB drive and rebuild the array, or if the 4TB drive fails no data is lost because both 2TB drives are fine, and I can just buy a 4TB drive and rebuild the array?

Is that how that works, can that even be done, and if so how would I set it up as my boot drive in linux?

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(separate array) Also if I had a 4TB gen 4 drive for parity and a gen 5 drive for data setup in RAID 1, would the whole array be as slow as the gen 4 drive when reading data or would I still be able to read at gen 5 (or similar) speeds?

[kokosnh]

RAID 5 - but the 4TB act as 2TB, so total space is 4TB… 

you can also just raid 0 the two 2TB SSD, and have the 4TB ssd as backup, 

I also have 2 x 2TB and 2 x 4TB ( nothing constructive to do with it )

 

[Electronics Wizardy]

 

You can do a mirror of the 2tb and then a raid 0 on top, or vice versa. 

 

You could also use something like btrfs that works well with mixed drive sizes.

 

 

[Raymond Gradzewicz]

12 minutes ago, kokosnh said:

RAID 5 - but the 4TB act as 2TB, so total space is 4TB… 

you can also just raid 0 the two 2TB SSD, and have the 4TB ssd as backup, 

I also have 2 x 2TB and 2 x 4TB ( nothing constructive to do with it )

 

wait, so I wouldn't need double the storage for a single drive to contain parity data for two drives?

[Raymond Gradzewicz]

6 minutes ago, Electronics Wizardy said:

 

You can do a mirror of the 2tb and then a raid 0 on top, or vice versa. 

 

You could also use something like btrfs that works well with mixed drive sizes.

 

 

You can stack raid arrays like that? Can you raid 0 two drives then raid 1 them to a third drive?

[Electronics Wizardy]

1 minute ago, Raymond Gradzewicz said:

You can stack raid arrays like that? Can you raid 0 two drives then raid 1 them to a third drive?

Yup you can do that. Make 2 mdadm array.

 

But really I'd just use a single 4TB drive and forget raid here if it was me.

[Eigenvektor]

1 hour ago, Raymond Gradzewicz said:

(separate array) Also if I had a 4TB gen 4 drive for parity and a gen 5 drive for data setup in RAID 1, would the whole array be as slow as the gen 4 drive when reading data or would I still be able to read at gen 5 (or similar) speeds?

RAID1 doesn't use parity, it uses mirroring. Both drives contain the exact same data. Technically you can get better read speeds, because reads can be parallelized. But that's generally only the case for hardware RAID, not software RAID.

 

mdadm has a "write-mostly" parameter that lets you define which disks should only be used for writes. It will avoid reading from these disks if at all possible, meaning it will prefer the non-write-mostly drive for read operations. So if you configure the Gen 4 drive as "write-mostly" it should typically prefer to read from the Gen 5 drive.

 

However, both Gen 4 and Gen 5 drives are so fast, you're unlikely to notice a difference in pretty much any general purpose use-case.

[porina]

What is the objective here? If it is to help ensure you have another copy of data, use the drives separately and set up a scheduled backup to copy them over. There will only be a small window of risk between data creation and duplication. Consider it as part of a wider backup strategy.