Hardware vs Software Raid1

iandoug · Posted: Tue Jun 08, 2021 5:17 pm Post subject: Hardware vs Software Raid1

Hi all

Finally got a new box (this one is 8 years old...) and trying to install.

I want to put /home on a pair of mirrored disks.

I've looked through various Gentoo LVM pages but don't see any references to enabling Raid1 in the BIOS ... is that not necessary or does that work entirely differently?

Thanks, Ian
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NeddySeagoon · Posted: Tue Jun 08, 2021 6:26 pm Post subject:

iandoug,

Raid1 writes the same thing to all the parts of the mirror set. There are no checksums to calculate.

BIOS raid is not hardware raid. Its software raid done by the BIOS. As the BIOS hides the real nature of the storage, its also called fakeraid. It looks like hardware raid but its not.
There is a reasonable summary.

You want software raid as provided by mdadm. That means that by default, you will need an initrd to start the raid set before root will be visible.
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Jaglover · Posted: Tue Jun 08, 2021 6:50 pm Post subject:

What are the chances of disk failure nowadays? Low, very low, I'd say, in particular if you keep an eye on its health. RAID-1 will add to read speed, which is already great with SSD, do you need this extra speed so badly? Other than that, there is no advantage. It won't protect against PEBKAC. I take a backup solution like rsnapshot over RAID-1 any time.
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iandoug · Posted: Tue Jun 08, 2021 7:05 pm Post subject:

@Neddy: so noted, thanks.

I don't use SSDs, only HDD.

I once had a desktop drive fail on me, can't risk it happening again. These are Dev boxes.

Have had several Seagate drives in a NAS box fail.

My tape drive is currently broken, terrified what the are going to charge to fix ...

I sleep better at night knowing my stuff is mirrored :-)

Will read up on mdadm again....

thanks, Ian
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figueroa · Posted: Wed Jun 09, 2021 3:33 am Post subject:

steve_v · Guru Joined: 20 Jun 2004 Posts: 388 Location: New Zealand

NeddySeagoon · Posted: Wed Jun 09, 2021 7:53 pm Post subject:

iandoug,

If you don't want to use an initrd to assemble your raid, there is a kernel option to do it but it only works with raid metadata version 0.90.
That must be specified explicitly when the raid set is created.

I've had two WD Greens fail in a raid5 set, 15 min apart. Luckily, they were still under warranty.
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Computer users fall into two groups:-
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szatox · Advocate Joined: 27 Aug 2013 Posts: 3137

Spanik · l33t Joined: 12 Dec 2003 Posts: 943 Location: Belgium

Jaglover · Posted: Thu Jun 10, 2021 2:00 pm Post subject:

I'm not arguing with anybody, but I always feel RAID-1 is a waste of hard drive. In this case, we hear there are development files what needs to be protected. There is a whole hard drive spinning to protect what, 100 MB of data, less? And this protection is not 100%, two drives can die together. If I had such a need I'd place the work directory in my server which has RAIDZ-2 and mount it over NFS. Every use case is different, though.
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pjp · Administrator Joined: 16 Apr 2002 Posts: 20067

Jaglover · Posted: Thu Jun 10, 2021 5:46 pm Post subject:

RAID-1 seems to me sort of an ancient solution to protect work directory. There are options to make snapshots locally and remotely. Gigabit and even faster networking makes remote storage transparent. I used the word "waste" because I think there are a better ways to use hard drives than in rather primitive RAID-1.
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pjp · Administrator Joined: 16 Apr 2002 Posts: 20067

Interesting. If I use RAID in this instance, it will be RAID-1.

I'm not aware of a local snapshot capability, unless you mean some sort of adhoc rsync thing. But that doesn't help where a second drive would be used as in the case of RAID-1 or as I'm likely to do with rsync. The second drive is absolutely worth having a reasonably up to date copy of data.

I'm also not aware of what can be accomplished with (presumably onsite) gigabit+ remote storage. As far as I know, that would require a separate system with at least one drive, which has already exceeded the cost and complexity of an in-system second drive solution. Then in the remote storage system, it would presumably be using some sort of RAID write hole solution (ZFS draid isn't recommended for small arrays).

As for waste, I understand your point. However, I don't see the "better" way that provides the same capabilities. I have a separate system to use for a "NAS" but haven't decided how it will be permanently set up (currently it uses rsync for internal copies between drives, but it isn't in active use, only for "urgent" situations). But whatever that ends up being, it is only a supplement to the internal capabilities of my other system with the rsync "mirror".

Someday I may get to a single drive solution that uses about half the disk for snapshots and then uses an external system for off-system copies, but I'd need new hardware for that :(.
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Anon-E-moose · Posted: Thu Jun 10, 2021 6:59 pm Post subject:

I don't use raid from my main system. But I have a couple of dual usb enclosures (hdd) on my backup server, and they both are set up for mirroring.
At the price for large hdd's, it hard to say it's a waste to have a 2nd copy.

Note: even with the mirrored storage, I don't entirely depend on it for major problems, as I also copy off both usb's onto another hdd as backup, it's not mounted, and it's simply for insurance.
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Jaglover · Posted: Thu Jun 10, 2021 7:45 pm Post subject:

Ralphred · Guru Joined: 31 Dec 2013 Posts: 501

NeddySeagoon · Posted: Fri Jun 11, 2021 5:43 pm Post subject:

Ralphred,

I lost one 4k disk block. I was very lucky.
The backups were my 1500 DVD collection.
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Computer users fall into two groups:-
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wwdev16 · n00b Joined: 29 Aug 2018 Posts: 52

If you have deadlines then raid can be a life-saver.

For me, I have raid1 & raid5 on the file server even though it is all ssd. I don't
want to be rushed fixing a storage failure and trying to rsync 3TB from backups.
It takes hours with usb3 connected hdds.

One of the ssds already has 15.5TB of nand writes in less than 2 years. Won't be
surprised if an ssd fails in the next two years while it's smart data says there's
nothing to worry about.

Zucca · Posted: Sat Jun 12, 2021 3:34 pm Post subject:

I'd avoid "bios"-raid at all costs. Others have mentioned why.
As for real hardware raid, I'd make sure I have spare hardware or some way to retrieve data if the rad controller dies.
Safest bet is to use pure software raid. mdraid or lvm2 have been my favourites. Also btrfs has limited raid functionality.
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pjp · Administrator Joined: 16 Apr 2002 Posts: 20067

dmpogo · Advocate Joined: 02 Sep 2004 Posts: 3267 Location: Canada

On my older desktops, my solution is to have a separate SSD disk to hold / partition with /usr, etc
128 GB is plenty for this purpose. You can get small NVMe for like $40 CAD (look for Transcend on amazon)

And put /home and whatever (*) on RAID1 mirrored spinners, as large as needed (and I need > 1 Tb )

No initird needed.

(*) whatever is typically /scratch, since most of my numerical output I do not backup, while /home I do.

iandoug · Posted: Tue Jun 15, 2021 9:20 pm Post subject:

Phew. For some reason, I didn't get emails that there were new posts.

Thanks for the viewpoints.

@Neddy, the root drive in this 8 year old box is WD Green, had no issues yet. But was a bit shocked when I saw the difference in warranty vs MD Black. Data disks are black, as are all three in new box.

Finally got Gentoo installed ( load shedding here got in the way), now trying to set up the RAID1.

I did this ONCE, 8 years ago, and don't remember much.

Trying to follow instructions here: https://wiki.gentoo.org/wiki/User:SwifT/Complete_Handbook/Software_RAID

but it fails at
mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/sdb1 /dev/sdc1

Disks look like

NeddySeagoon · Posted: Tue Jun 15, 2021 9:55 pm Post subject:

iandoug,

iandoug · Posted: Wed Jun 16, 2021 7:45 am Post subject:

iandoug · Posted: Wed Jun 16, 2021 7:20 pm Post subject:

Appears correct now ...