3 HDDs in Raid 5 or 2 HDDs in Raid 1? And why are these SO cheap?

PowerPCFan · March 31

Should I get 3x 2TB drives in RAID 5 for 4TB usable storage? or 2x 4TB drives in RAID 1, also for 4TB usable storage?

And why are these drives so cheap? What is their intended use case and why are they half the cost of other 2tb drives? https://www.amazon.com/2TB-Datacenter-Hard-Disk-Drive/dp/B00CYSYZTS/ref=sr_1_5

Eigenvektor · March 31

They have the same amount of fault tolerance. The primary advantage of RAID 5 is that you only lose 33% of storage capacity compared to 50% with RAID 1. RAID 1 can give some performance advantages.

If you want a more in depth comparison:

https://www.diskinternals.com/raid-recovery/raid-1-vs-raid-5/

Kilrah · March 31

57 minutes ago, PowerPCFan said:

why are they half the cost of other 2tb drives

If you look at this seller's other products HDDs are a bit out of place, they have a 4TB one for the same price, reviews suggest they're either used/reconditioned and that you may not get the pictured model.

So seems like a slightly shady seller.

That's also twice the price / TB of larger drives so not really a good deal unless you have limited budget but that's usual.

MiszS · March 31

i would choose raid 5, because you can lose 1 drive just like in raid 1, but only 33% (or 25% with 4 drives) of the space is used for redundancy, sure it has technically a higher chance to fail because it has 3 drives instead of 2, but i don't think it matters, when you still only have to replace 1 drive

StDragon · March 31

23 minutes ago, MiszS said:

i would choose raid 5, because you can lose 1 drive just like in raid 1, but only 33% (or 25% with 4 drives) of the space is used for redundancy, sure it has technically a higher chance to fail because it has 3 drives instead of 2, but i don't think it matters, when you still only have to replace 1 drive

^ This.

Also, depending on the type of RAID5, you can add another drive to extend the volume with some caveats. For example the ZFS equivalent of RAID5 is known as RAID-Z1 can't be extended whereas BTRFS doesn't have this limitation.

For a breakdown of non-standard RAID levels, here's a good synopsis.
https://en.wikipedia.org/wiki/Non-standard_RAID_levels

Kilrah · March 31

14 minutes ago, StDragon said:

whereas BTRFS doesn't have this limitation

BTRFS still only officially supports RAID1/RAID0/single. RAID5/6 have been "experimental, don't use" for years.

StDragon · March 31

42 minutes ago, Kilrah said:

BTRFS still only officially supports RAID1/RAID0/single. RAID5/6 have been "experimental, don't use" for years.

Good call. I've only used BTRFS for RAID1, but have known RAID5/6 to be available. Didn't know it was marked "unstable" of a feature.

Anyways, seems RAID is pretty much a solved problem if software and vendors would adhere to the Disk Data Format (DDF) standard per SNIA.