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Make a raid 5 with two almost full disk and another one empty (lemm.ee)
submitted 4 months ago* (last edited 4 months ago) by loboaureo@lemm.ee to c/selfhosted@lemmy.world
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Hello,

I am going to upgrade my server, taking advantage of the fact that I am going to be able to put more hard disks, I wanted to take advantage of this to give a little more security (against loss) to my data.

Currently I have 2 hard drives in ext4 with information, and wanted to buy a third (same capacity all three) and place them in raid5, so that in the future, I can put more hard drives and increase the capacity.

Due to economic issues, right now I can only buy what would be the third disk, so it is impossible for me to back up the data I currently have.

The data itself is not valuable, in case any file gets corrupted, I could download it again, however there are enough teras (20) to make downloading everything a madness.

In principle I thought to put on this server (PC) a dietpi, a trimmed debian and maybe with mdadm make the raid. I have seen tutorials on how to do it (this for example https://ruan.dev/blog/2022/06/29/create-a-raid5-array-with-mdadm-on-linux ).

The question is, is there any way without having to format the hard drives with data?

Thank you and sorry for any mistakes I may make, English is not my mother language.

EDIT:

Thanks for yours answers!! I have several paths to investigate.

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[-] malaknight@programming.dev 5 points 4 months ago* (last edited 4 months ago)

So I see a few problems with what you want, for a raid5 setup you will need at least four drives, since your information is striped against 3 and then the fourth is a parity drive. with 3 drives you have an incredibly high likelyhood of losing your parity drive.

To my knowledge, you will need to wipe the drives to put them in any kind of raid. Since striping is essentially making custom sections of blocks; I don't think mdadm is smart enough to also move data files as well.

I would really recommend holding off on your project till you can back up the information, and get a fourth drive. I know there is a lot of talks between raid5 and raid6, but for me I really prefer the peace of mind that raid6 gives.

Edit: seems like it is possible with at least raid 1:https://askubuntu.com/questions/1403691/how-can-i-create-mdadm-raid1-without-losing-data

[-] catloaf@lemm.ee 9 points 4 months ago

You can do RAID 5 with three disks. It's fine. Not ideal, but fine.

My biggest concern is what OP is using as a server. If these disks are attached via USB, they are not going to have reliable connections, and it's going to trigger frequent RAID rescans and resyncs any time one of the three disks drops out. And the extra load from that might cause even more drops.

[-] just_another_person@lemmy.world 4 points 4 months ago

I reread this a few times after seeing your comment, but still missing where USB was mentioned. Am I blind?

[-] catloaf@lemm.ee 3 points 4 months ago

They didn't say USB, but they did say dietpi. I've never played with a rpi, but I don't think they have SATA or SAS ports, only USB.

[-] just_another_person@lemmy.world 2 points 4 months ago

Ah, he said PC, so I just assumed he wanted the distribution on x86. I see where you're coming from though.

[-] loboaureo@lemm.ee 1 points 4 months ago

Yes, dietpi is main for SBC, but also has an iso for PCs, its and old computer with 6 sata ports

this post was submitted on 18 Jun 2024
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