How do you (software) RAID?

eccerr0r · Posted: Fri Jul 01, 2022 6:19 pm Post subject: How do you (software) RAID?

RAIDs, or Redundant Array of (Inexpensive/Independent) Disks is a way to use multiple disk drives together to provide redundancy or speed improvement, or even both. And you can build them in Linux with software.

Do you use RAID on one of your Gentoo systems, and what kind?

I use LVM over MDRAID5 on 3 disks at the moment, used to have a 4-disk but not any more. I even have another LVM over MDRAID5 on 2 hard disks (a degenerate (not degraded!) RAID5 that basically functions as a slow RAID1, was meant to grow it to a normal RAID5 if I got a third disk. Not sure this is possible on LVM-RAID5 or not, but oh well...)
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NeddySeagoon · Posted: Fri Jul 01, 2022 6:41 pm Post subject:

eccerr0r,

I use raid1 for /boot and or the EFI Partition because EFI is broken by design in that respect.

Then mdadm raid5 with LVM over the top on rotating rust.
That mix isn't in your poll.

I did look at LVM doing raid 5 for itself but

eccerr0r · Posted: Fri Jul 01, 2022 7:19 pm Post subject:

Actually I did... wrote "lowest level", so you're using MD at a lower level than LVM, so you're using MDRAID (the same way I'm using md/lvm!)

I think I virtually/inadvertently wrote a primer on how to do create/use LVMRAID5 on another thread which sort of made me wonder how often people use this method, hence this poll.
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NeddySeagoon · Posted: Fri Jul 01, 2022 7:22 pm Post subject:

eccerr0r

I can't choose both Raid1 and Raid5 in your poll.
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Zucca · Posted: Fri Jul 01, 2022 7:42 pm Post subject:

lvmraid 1,5 and 6

;)
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mike155 · Posted: Fri Jul 01, 2022 10:22 pm Post subject:

I don't use RAID on my Gentoo systems. I use Subversion, Git and cron-jobs calling tar to make backups of my data.

eccerr0r · Posted: Fri Jul 01, 2022 11:35 pm Post subject:

death-magnet · n00b Joined: 01 Jul 2022 Posts: 9

For the longest time I had a raid0 setup on my laptop. It came with a raid controller specifically for this. (a msi gaming laptop from almost 10 years ago) But when I tried a new distro a while back, no matter what I couldn't get its installer (calamares) to correctly see and interact with the disks. mdadm was enabled, prepartitioned so no screwy business there. Nope.

Apparently for whatever reason that setup did not like being installed to a raid setup. So I moved some files around and disabled it. It was raid0. I wanted speed, not redundancy. I keep backups elsewhere anyway. These old SSDs are still decent on their own, but definitely perform better under the raid0.

Now that I'm messing with gentoo I've kinda got the mind to turn that back on and see if it will turn this already insanely fast monstrosity up to 11.

I'm quite confident I can set up and install it with the raid in place. I may have to unsimplify my kernel and go with an initramfs to make it work though. I kinda like simplicity. Less stuff to go wrong.

pa4wdh · l33t Joined: 16 Dec 2005 Posts: 811

I've voted for "MDRAID 1, 1+0, 0+1". I use MDRAID 1 on my server with LVM on top (and LUKS on top of some LV's). I use 0.9 metadata so the kernel can autodetect the raid arrays and / can be on raid without the need for an initrd.

How many using MDRAID actually follow this advice? https://raid.wiki.kernel.org/index.php/Choosing_your_hardware,_and_what_is_a_device%3F#TLER_and_SCT.2FERC
I now have two 1TB Samsung 860 EVO's in software raid which have the SCT/ERC feature and i'm looking for a new SSD which also implements it but it seems to be removed on newer models, does anyone know one?
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sabayonino · Veteran Joined: 03 Jan 2012 Posts: 1012

I've MD - RAID 1 for my private Docs

and MD - RAID 5 (3 x 1,5 TB) for Working docs and other stuffs

and Minor things on cloud.

I've 2 hardware raid controllers (4 x sata 2.) that I don't use anymore
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NeddySeagoon · Posted: Sat Jul 02, 2022 11:04 am Post subject:

death-magnet,

Built in Raid controllers, except on servers are fakeraid. Very few work with mdadm. They usually need sys-fs/dmraid.
For raid0, there is no parity to calculate, so a real hardware raid controller does very little.
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lekto · Posted: Sat Jul 02, 2022 11:20 am Post subject:

RAID1 on SSDs wherever I can.
Right now:
main PC - good quality about 256GB NVME + 512GB Aliexpress quality NVME (half of it is unpartitioned) using mdraid.
main laptop - two 512GB SSDs from Aliexpress with ZFS mirror on both.
Currently waiting:
NAS - 32GB industrial SSD in mirror with one disk (I don't have and can't buy second same disk anywhere), I want to reinstall system this year and put ZFS mirror for root.
Internet gateway - when OpenBSD 7.2 come out I want to put two SSDs (probably again from Aliexpress) and make it mirror raid.

I want to have every SSD I have in mirror because I worked in PC shop and I saw how fragile they are. I had many customers with failed SSD that just suddenly stopped working (with decent brands like Crucial or Kingston) and all data were gone. When HDD is failing at least you get some warnings (poor performance, noise etc.) and you can save your data. My last broken NVME just stopped working without warning, after restart it was working about 1.5min (if I remember correctly) and disappeared, recovering data from it was… fun, had to speedrunning running ddrescure, and restarting PC many times. Also at beginning of this year I had two failed SSDs: 32GB industrial Sandisk and 120GB Adata, on both btrfs was throwing errors in dmesg, but smart was clean, I had to use badblocks to find problems and after this smart was still clean.

eccerr0r · Posted: Sat Jul 02, 2022 2:04 pm Post subject:

I use whatever drives I can get my hands on to, but TLER / SCTERC would be nice. I think the ones I have happen to have TLER anyway.

I would think that SSDs this is not an issue, it can either read a block or not, there's no retry unlike a mechanical hard disk...

And Zucca, vote the array that you do the most read/writes to! Else lvm-raid should be deleted as nobody uses it! :D

(come to think of it I probably should have added raid-z options ... but anyway...)
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C5ace · Posted: Sat Jul 02, 2022 3:06 pm Post subject:

I use RAID 1 for /boot and RAID 5 for /, /home and swap on 3x2TB rotating rust.
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MrRoy3 · n00b Joined: 10 Feb 2022 Posts: 53 Location: Canada

The poll is missing ZFS/BTRFS RAID options

For my NAS, I use BTRFS RAID 5 (with metadata on RAID1).
I think the write hole issue is overblown and much rarer than people like to believe, so I take the "risk" of using BTRFS RAID 5, despite all the warnings.

eccerr0r · Posted: Sat Jul 02, 2022 7:56 pm Post subject:

yeah, forgot about that, mentioned it just a few hours ago for the filesystem options. Alas seems this is a rarity too since nobody mentioned they were using it before now... likewise LVM-RAID, it's pretty much MD RAID, might well be since it's the oldest I think...

The write hole is a risk, it's not completely overblown. The thing is that most people aren't constantly writing to their disks with random irreplaceable stuff, so it's rarely an issue. But if you just so happen to be writing that bit of data and it's not consistent due to power outage our whatnot...
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MrRoy3 · n00b Joined: 10 Feb 2022 Posts: 53 Location: Canada

eccerr0r · Posted: Sun Jul 03, 2022 1:30 am Post subject:

MrRoy3 · n00b Joined: 10 Feb 2022 Posts: 53 Location: Canada

Tout · n00b Joined: 18 Jul 2020 Posts: 33

Wow. I'm a bit shocked. As per my understanding, raid configurations are not safe to use on their own. I thought that data corruption can occur unnoticed, and be carried to all disks, making data corruption just redundant

But hey, I could be wrong of course. If I am wrong, I am superstitious. My superstition than gives me BTRFS. And yes, I am using raid in that for my data disks

Do not now what kind, but I have three disks of different sizes, where one can fail

So it's not 1 or 0 I guess, might be a kind of 5

For my root I just use one partition, BTRFS snapshots and offline backups.

I hope for you that I am superstitious and wrong of course, if you are running raid on it's own without other safety measures. I was also in the understanding that the unsafety of raid on its own was common knowledge. How one can live in a bubble

Is my understanding of raid is not a backup also one of my bubbly things? Or is that one indeed common?

Zucca · Posted: Sun Jul 03, 2022 7:37 am Post subject:

eccerr0r · Posted: Sun Jul 03, 2022 12:25 pm Post subject:

John R. Graham · Posted: Sun Jul 03, 2022 11:22 pm Post subject:

Hardware RAID 6 only with Adaptec controllers at the moment, but software RAID is in my future: I'm planning a RAIDz2 array.

- John
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figueroa · Posted: Mon Jul 04, 2022 3:23 am Post subject:

eccerr0r, you write, "I use LVM over MDRAID5" though that is not an obvious choice in your poll. I think poll lacks clarity.
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eccerr0r · Posted: Mon Jul 04, 2022 3:07 pm Post subject:

LVM over MDRAID5 means LVM on top of MDRAID5, which was the traditional method prior to LVM adding internal RAID support which I call LVM-RAID.

Basically if you use mdadm to maintain your RAID, you're using MDRAID.
If you're using lvconvert, lvcreate, pvcreate, etc. to maintain your RAID you're using LVM-RAID.

Mainly I'm wondering who's using internal to lvm RAID support. But clearly I forgot about adding an option for internal to filesystem RAID support like zfs, etc...
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