this post was submitted on 18 Jun 2024
25 points (100.0% liked)

Selfhosted

45747 readers
845 users here now

A place to share alternatives to popular online services that can be self-hosted without giving up privacy or locking you into a service you don't control.

Rules:

  1. Be civil: we're here to support and learn from one another. Insults won't be tolerated. Flame wars are frowned upon.

  2. No spam posting.

  3. Posts have to be centered around self-hosting. There are other communities for discussing hardware or home computing. If it's not obvious why your post topic revolves around selfhosting, please include details to make it clear.

  4. Don't duplicate the full text of your blog or github here. Just post the link for folks to click.

  5. Submission headline should match the article title (don’t cherry-pick information from the title to fit your agenda).

  6. No trolling.

Resources:

Any issues on the community? Report it using the report flag.

Questions? DM the mods!

founded 2 years ago
MODERATORS
ruud@lemmy.world
Loki@lemmy.world
CannaVet@lemmy.world
devve@lemmy.world
HybridSarcasm@lemmy.world
HybridSarcasm@lemmy.hybridsarcasm.xyz
25
Make a raid 5 with two almost full disk and another one empty (lemm.ee)
submitted 9 months ago* (last edited 9 months ago) by loboaureo@lemm.ee to c/selfhosted@lemmy.world
32 comments fedilink hide all child comments
 

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.

all 48 comments
sorted by: hot top controversial new old
[–] SwingingTheLamp@midwest.social 22 points 9 months ago (2 children)

This is madness, but since this is a hobby project and not a production server, there is a way:

  • Shrink the filesystems on the existing disks to free up as much space as possible, and shrink their partitions.
  • Add a new partition to each of the three disks, and make a RAID5 volume from those partitions.
  • Move as many files as possible to the new RAID5 volume to free up space in the old filesystems.
  • Shrink the old filesystems/partitions again.
  • Expand each RAID component partition one at a time by removing it from the array, resizing it into the empty space, and re-adding it to the array, giving plenty of time for the array to rebuild.
  • Move files, shrink the old partitions, and expand the new array partitions as many times as needed until all the files are moved.

This could take several days to accomplish, because of the RAID5 rebuild times. The less free space, the more iterations and the longer it will take.

[–] Revan343@lemmy.ca 7 points 9 months ago

That is madness. I love it

[–] ChojinDSL@discuss.tchncs.de 9 points 9 months ago (1 children)

Not really with mdadm raid5. But it sounds like you like to live dangerously. You could always go the BTRFS route. Yeah, I know BTRFS Raid56 "will eat your data", but you said it's nothing that important anyways. There are some things to keep in mind when running BTRFS in Raid5, e.g. scrub each disk individually, use Raid1c3 for metadata for example.

But basically, BTRFS is one of the only filesystems that allows you to add disks of any size or number, and you can convert the profile on the fly, while in use. So in this case, you could format the new disk with BTRFS as a single disk. Copy over stuff from one of your other disks, then once that disk is empty, add it as a additional device to your existing BTRFS volume. Then do the same with the last disk. Once that is done, you can run a balance convert to convert the single profile into a raid5 data profile.

That being said, there are quite a few caveats to be aware of. Even though it's improved a lot, BTRFS's Raid56 implementation is still not recommended for production use. https://lore.kernel.org/linux-btrfs/20200627032414.GX10769@hungrycats.org/

Also, I would STRONGLY recommend against connecting disks via USB. USB HD adapters are notorious for causing all kinds of issues when used in any sort of advanced setup, apart from temporary single disk usage.

[–] loboaureo@lemm.ee 1 points 9 months ago

Interesting, i think it will be made for my usecase. i'll check it

Thanks for your answer!!

[–] jaypg@lemmy.jaypg.pw 6 points 9 months ago (1 children)

Traditional RAID isn’t very flexible and is meant/easiest for fresh disks without data. Since you’ve already got data in place, look into something like SnapRAID.

[–] B0rax@feddit.de 2 points 9 months ago

And mergerFS

[–] malaknight@programming.dev 5 points 9 months ago* (last edited 9 months ago) (2 children)

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 11 points 9 months ago (1 children)

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.

[–] neidu2@feddit.nl 5 points 9 months ago* (last edited 9 months ago) (2 children)

Seconding this. For starters, when tempted to go for Raid5, go for Raid6 instead. I've had drives fail in Raid5, and in turn have a second failure during the increased I/O associated with replacing a failed drive.

And yes, setting up RAID wipes the drives. Is the data private? If not, a friendly datahoarder might help you out with temporary storage.

[–] BearOfaTime@lemm.ee 5 points 9 months ago (3 children)

I run RAID5 on one device.... BUT only because it replicates data that's on 2 other local devices AND that data is backed up to a cloud storage.

And I still want it to be RAID 6.

[–] neidu2@feddit.nl 7 points 9 months ago* (last edited 9 months ago) (2 children)

Story time!

In this one production cluster at work (1.2PB across four machines, 36 drives per machine) everything was Raid6, except ONE single volume on one of the machines that was incorrectly set up as Raid5. It wasn't that worrysome, as the data was also stored with redundancy across the machines in the storage cluster itself (a nice functionality of beegfs), but it annoyed the fuck out of me for the longest time.

There was some other minor deferred maintenance as well which necessitated a complete wipe, but there was no real opportunity to do this and rebuild that particular RAID volume properly until last spring before the system was shipped off to Singapore to be mobilized for a survey. I planned on getting it done before the system was shipped, so I backed up what little remained after almost clearing it all out, nuked the cluster, disassembled the raid5, and then started setting up everything from scratch. Piece of cake, right?

shit

That's when I learned how much time it actually takes to rebuild a volume of 12 disks, 10TB each. I let it run as long as I could before it had to be packed up. After half a year of slow shipping it finally arrived on the other side of the planet, so I booked my plane ticket and showed up a week before anyone else just so I could connect power and continue the reraiding before the rest of the crew showed up. Basically, pushing a few buttons, followed by a week of sitting at various cafes drinking beer. Once the reraid was done, reclustering was done in less than an hour, and restoring the folder structure backup was a few hours on top of that. Not the worst work trip I've had, except from some unexpected and unrelated hardware failures, but that's a story for another day.

Fun fact: While preparing the system for shipment here in Europe, I lost one of my Jabra bluetooth buds. I searched fucking everywhere for hours, but gave up on finding it. I found it half a year later in Singapore, on top of the server rack, surprised it hadn't even rolled down. It really speaks to how little these huge container ships roll.

[–] BearOfaTime@lemm.ee 2 points 9 months ago* (last edited 9 months ago) (1 children)

Haha, everything about that story is awesome, right down to the lost and found Jabra ear bud (does Jabra exist any more? At one time their ear pieces were the best).

Yes, re-silvering takes fucking forever. Even with my little setups (a few TB), it can take a day or two to rebuild one drive in an array. One.

I can only imagine how long a PB array would take.

[–] neidu2@feddit.nl 2 points 9 months ago* (last edited 9 months ago)

Jabra still exists yes. I'm still using Jabra, although I'm using a pair that I bought after I thought that one earbud was gone forever. I still use the older ones, which was Jabra Elite 4, but only with my PC, as its battery took a hit after those 6 months at sea. I currently main Jabra Active 7 or something like that, and I quite like them. I noticed that the cover doesn't stay very attached after a few proper cleans, but nothing a drop of glue doesn't fix. What I really like about the ones I currently use is that they're supposedly built to withstand sweat while training. I don't work out, but it would seem that those who do sweat A LOT, as I can wear mine while showering without any issues.

As for resilvering, the RAIDs are only a small fraction each of the complete storage cluster. I don't remember their exact sizes, but each raid volume is 12 drives of 10TB each. Each machine has three of these volumes. Four machines total contributes all of its raid volumes to the storage cluster for 1.2PB of redundant storage (although I'm tempted to drop the beegfs redundancy, as we could use the extra space, and it's usually fairly hassle free to swap in a new server and move the drives over).

EDIT: I just realized that I have this Jabra confference call speaker attached to the laptop on which I'm currently typing. I mostly use it for discord while playing project zomboid with my friends, though. I run audio output elsewhere, as the jabra is mono only.

[–] loboaureo@lemm.ee 1 points 9 months ago

If i goes to raid5 i lost one disk of space, to go to raid6 i have to lost 2 disks.

Its a pesonal proyect, and the motherboard has only 6satas, one of them used by the SO disk, and i want to be able of upgrade it in a future...

[–] catloaf@lemm.ee 2 points 9 months ago

It's possible to convert drives to RAID in-place... but strongly discouraged.

Since OP will have a blank drive, they could play musical chairs by setting up a new RAID on the new empty drive, copy data from one drive, wipe that drive, grow the array, copy data from the third drive, wipe, grow... But that's going to take a long time, and you'll have to keep notes about where you are in the process, lest you forget which drive is which over the multiple days this will take.

[–] MalReynolds@slrpnk.net 4 points 9 months ago (1 children)

I'd suggest you move toward a backup approach ("RAID is not a backup") first. Assuming you have 2x10Tb, get a 3rd and copy half of your files to it, disconnect it, and now half your files are protected. Save, get another, copy the other half, now all your files are protected. If you're trying to do RAID on USB, don't, you are already done, otherwise (using SATA or better) you can proceed to build your array in an orderly fashion.

[–] loboaureo@lemm.ee 3 points 9 months ago (1 children)

I know its not backup, but, for me, its the sweet point between money and security. Not only for this 2 hard disk, also for the capacity of add more HDs and don't have all redundancy.

Thanks for your answer!!

[–] possiblylinux127@lemmy.zip 2 points 9 months ago

I will say it three times, Raid isn't a backup

Raid isn't a backup

Raid isn't a backup

Seriously though it shouldn't give much peace of mind. All raid does is add a little resistance to hardware failures. If you mistakingly delete files you are hosed. If your hardware causes corruption you are hosed. If something happens to your computer such a physical abuse your drives are likely going to be damaged which will also mean that you may be hosed. If one drive dies and then the other drives dies before you move your data over you are also hosed.

The big take away is that Raid only really buys time. It can prevent downtime but it will not save you.

[–] butitsnotme@lemmy.world 4 points 9 months ago* (last edited 9 months ago)

My recommendation would be to utilize LVM. Set up a PV on the new drive and create an LV filling the drive (wit an FS), then move all the data off of one drive onto this new drive, reformat the first old drive as a second PV in the volume group, and expand the size of the LV. Repeat the process for the second old drive. Then, instead of extending the LV, set the parity option on the LV to 1. You can add further disks, increasing the LV size or adding parity or mirroring in the future, as needed. This also gives you the advantage that you can (once you have some free space) create another LV that has different mirroring or parity requirements.

[–] MangoPenguin@lemmy.blahaj.zone 3 points 9 months ago* (last edited 9 months ago) (1 children)

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

MergerFS would let you pool drives without needing to set up RAID and format them.

Then add SnapRAID on top of that for parity.

[–] signalsayge@lemm.ee 1 points 9 months ago

This is how I do it. No striping, normal partitions, different hard drive sizes, pretty easy. This way makes upgrades super easy too. Currently running 76TB mergerfs with 2 14TB Snapraid parity drives.

[–] possiblylinux127@lemmy.zip 2 points 9 months ago

If you used ZFS this would be easier to fix. I would recommend switching to it.

It sounds like you need another disk. I know that isn't always possible and if it isn't delete enough data to to copy it over to a single disk. Without backups you are destined to lose your data anyway.

For a ZFS three disk I would go with raidz1 as that will give you one drive for redundancy.

[–] signalsayge@lemm.ee 2 points 9 months ago

Just use Snapraid & MergerFS. No special Hardware required and you don't need to change what is on your disks.

From a quick search: https://perfectmediaserver.com/02-tech-stack/snapraid/

[–] Decronym@lemmy.decronym.xyz 1 points 9 months ago* (last edited 9 months ago)

Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread:

Fewer Letters More Letters
LVM (Linux) Logical Volume Manager for filesystem mapping
RAID Redundant Array of Independent Disks for mass storage
SATA Serial AT Attachment interface for mass storage
SBC Single-Board Computer
ZFS Solaris/Linux filesystem focusing on data integrity

5 acronyms in this thread; the most compressed thread commented on today has 15 acronyms.

[Thread #815 for this sub, first seen 18th Jun 2024, 18:45] [FAQ] [Full list] [Contact] [Source code]