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iandoug
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PostPosted: Tue Jun 08, 2021 5:17 pm    Post subject: Hardware vs Software Raid1 Reply with quote

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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PostPosted: Tue Jun 08, 2021 6:26 pm    Post subject: Reply with quote

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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PostPosted: Tue Jun 08, 2021 6:50 pm    Post subject: Reply with quote

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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PostPosted: Tue Jun 08, 2021 7:05 pm    Post subject: Reply with quote

@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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PostPosted: Wed Jun 09, 2021 3:33 am    Post subject: Reply with quote

Jaglover wrote:
What are the chances of disk failure nowadays?

I just had an older 500 GB primary hard drive in a remote server come to a screeching halt only two weeks ago (probably head crash or other mechanical failure). Hardware failure is a fact of live. I live by my multiple, redundant, rotating backups.

I had my local guy install a new primary drive then boot from a flash drive (You have to plan ahead.). I restored backups, installed GRUB, and back in service.

Had a quieter, but complete, failure on a remote desktop computer with newer drives happen just a few weeks before that.
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PostPosted: Wed Jun 09, 2021 7:52 am    Post subject: Reply with quote

Jaglover wrote:
What are the chances of disk failure nowadays? Low, very low, I'd say, in particular if you keep an eye on its health.

For spinning rust, I'd say about the same as ever. I've seen plenty of sudden, warning-devoid disk failures, and IMO anything that SMART "health" report tells you should be taken with a truly brobdingnagian grain of salt.
Stats and sensors are all good, but failures are stupidly difficult to predict in a system as complex and highly-strung as a modern high-capacity disk drive.

I don't have anywhere near as much experience with SSDs, but I get the impression reliability is considerably better. Apparently backblaze agrees. That said I have had a couple of SSDs die suddenly on me too, again with no advance warning.

Last I looked, "drives" still lives right beneath "fans" on the list of things I see fail most often.

Jaglover wrote:
I take a backup solution like rsnapshot over RAID-1 any time.

RAID ~= redundancy. Backups ~= recovery.
What you want is both, RAID so that your system keeps on trucking when a drive dies, and backups in case you foolishly rm -rf / or somehow trash your RAID... Or, ya know, the building burns to the ground.

Jaglover wrote:
Other than that, there is no advantage.
How about uptime?
In many situations, waiting even a few minutes for a drive to be replaced is unacceptable. RAID handles that. RAID keeps the database up and the customers quiet while it activates one of your spare disks and summons a technician to replace the failed unit.

Clearly for a personal system uptime isn't such a big deal, but even if all it means is I don't have to deal with the irritation of an out-of-service machine while I replace a drive and restore from backup, that's still a pretty sweet advantage.


To return to the OP...

iandoug wrote:
don't see any references to enabling Raid1 in the BIOS


You probably want to completely disable any RAID setting in any BIOS, and use mdadm to set up software RAID.
Unless you have very specific requirements you'll likely see no benefit from a hardware RAID controller - even if consumer motherboards shipped with them, which they generally don't.
On a modern machine software RAID is faster than anything but the most eye-wateringly expensive add-in hardware, it's usually more flexible, and (most importantly IMO) your data isn't hostage to some potentially irreplaceable proprietary board - just plug your drives into a random GNU/Linux box and assemble the array.

The BIOS RAID on most consumer motherboards is the worst of both worlds - you're hostage to that board (and maybe even specific BIOS revisions), and everything is done on the host CPU anyway.
It is supported via dmraid if you want to go there, but frankly the only use case I can think of for it is sharing an array with Windows... a concept which does not excite me in the least. *shudder*
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PostPosted: Wed Jun 09, 2021 7:53 pm    Post subject: Reply with quote

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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PostPosted: Wed Jun 09, 2021 9:21 pm    Post subject: Reply with quote

NeddySeagoon wrote:

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.
yeah, and since it places superblock at the end of your device, it doesn't move the filesystem, so you can use a very simple bootloader too (like in: not raid-aware). No need for grub2.
Quote:

I've had two WD Greens fail in a raid5 set, 15 min apart. Luckily, they were still under warranty.
Was your data under warranty too?
Anyway, that's why I always recommend mixing drives from different manufacturers (or at least batches) and mixing new drives with used ones in a single raid.
They are less likely to fail at the same time, which would be a much bigger problem than a single disk failing early.
Yes, backups, I know. Still, I prefer hot-swapping the failed drive and resilvering on the fly than having that service forced offline until manually started recovery completes.
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PostPosted: Thu Jun 10, 2021 1:38 pm    Post subject: Reply with quote

Jaglover wrote:
What are the chances of disk failure nowadays? Low, very low, I'd say, in particular if you keep an eye on its health.


I have at least one a year that fails. Doesn't make much difference in HD or SSD. Right now one in the old RAID5 is dead. The one before was the SSD containing Gentoo. Even with each raid array having a fan in front of it and one for the SSD's.

I agree on RAID to protect against the occasional HD failure to keep running and save those last files that didn't make it to backup. It doesn't replace backups, it just buys you time. But when a single HD of the RAID set fails I replace them all. I know there are things to be said to not use all the same ones and/or different ages but I tried it once and performance took a hit. So i'm back in "all the same drives" camp.
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PostPosted: Thu Jun 10, 2021 2:00 pm    Post subject: Reply with quote

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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PostPosted: Thu Jun 10, 2021 4:54 pm    Post subject: Reply with quote

Jaglover wrote:
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.
I'm sort of in agreement with you. Not with the "waste" of a drive, but more because I don't like the complexity of RAID on the hardware I've owned (for enterprise HW, I'd use RAID).

I bought 2 drives to replace a dying drive, and I still haven't decided if I'm going to use RAID. I'm leaning towards an rsync solution for keeping them as in sync as they need to be. I guess I could just physically label which drive was which, and that would make dealing with RAID a little easier in the event of failure. Then I'd also need a guide on how to replace a drive, and the guide would need to be quickly accessible to address a failure. While writing all of that, I started to think maybe I should just use RAID, but eww. I miss ZFS.
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PostPosted: Thu Jun 10, 2021 5:46 pm    Post subject: Reply with quote

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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PostPosted: Thu Jun 10, 2021 6:54 pm    Post subject: Reply with quote

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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PostPosted: Thu Jun 10, 2021 6:59 pm    Post subject: Reply with quote

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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PostPosted: Thu Jun 10, 2021 7:45 pm    Post subject: Reply with quote

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

Right.
However, this is not about right and wrong. This is about adjusting to actual conditions, diversity and resourcefulness. :)
In ancient Rome with no networking and USB storage and all wonders of 21st century RAID-1 was maybe the only protection against hard drive failure.
Nowadays we have fast networking, USB storage, etc. We have filesystems with built-in snapshot capability.
Having two computers connected on LAN already creates interesting new possibilities. More computers - more viable solutions. For instance, What is better, having four computers all with RAID-1 or one with RAID-6 and others using its storage over LAN?
And what about USB flash drive as a local backup media? Using hard links as rsnapshot does you can have 100 backups taking up only a little more than one single backup. You can use two or more USB flash drives to get better protection than RAID-1 while it takes less space, less energy and costs less.
Just add here whatever your creativity can produce ...
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PostPosted: Fri Jun 11, 2021 1:52 am    Post subject: Reply with quote

NeddySeagoon wrote:
I've had two WD Greens fail in a raid5 set, 15 min apart
WD Greens .. in a raid5
No sympathy for the self inflicted data loss Neddy :P

The stuff I build for is short term archival storage, this is a common conversation:
Quote:
So, you fill this drive up every 90 days, and then start overwriting. Then one of the drives in the raid failed, you sent and engineer to swap out the drive. Then you asked the other drives to read 90 days of data in 24 hours. Now you're wondering why a second disk, the same age as the first, with an identical historic usage pattern, from the same manufacturer, probably the same batch, failed during the rebuild?

For the WORO stuff we do, the half offset LAID's are a much better idea (they are akin to small, mirrored MAID's).
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PostPosted: Fri Jun 11, 2021 5:43 pm    Post subject: Reply with quote

Ralphred,

I lost one 4k disk block. I was very lucky.
The backups were my 1500 DVD collection.
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PostPosted: Sat Jun 12, 2021 6:10 am    Post subject: Reply with quote

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.
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PostPosted: Sat Jun 12, 2021 3:34 pm    Post subject: Reply with quote

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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PostPosted: Mon Jun 14, 2021 10:32 pm    Post subject: Reply with quote

Jaglover wrote:
However, this is not about right and wrong. This is about adjusting to actual conditions, diversity and resourcefulness. :)
I agree that it isn't about right and wrong.

Jaglover wrote:
What is better, having four computers all with RAID-1 or one with RAID-6 and others using its storage over LAN?
Depends on your goal. They aren't comparable solutions. I consider the complexity of RAID-6 on consumer hardware to be a liability. I only consider RAID-1 to be an online backup that protect against data loss between off-system backups. In that scenario, your RAID-6 system is not helpful. Instead of your RAID-6 solution, I have another system that I'll likely use in RAID-1 configuration (possibly 2 pairs of mirrors) to provide off-system backups. Also, depending on the details, a RAID-6 solution seems likely to concentrate more heat into a single system, which may potentially generate more fan noise.

Jaglover wrote:
And what about USB flash drive as a local backup media?
Depending on its purpose, that doesn't seem like an improvement over using RAID-1. My understanding is that the flash memory in thumb drives has never been great for long-term writes. I haven't kept up with any improvements, so I've always tried to use them as modern WORM drives (Write Occasionally Read Mostly). I have some portable USB HDDs that I may enlist for something, though I'm not sure what. In general I don't like the clutter of external devices, though sometimes they're convenient. I do have an SD card of some type that disappears into the laptop, so that's handy. I need to migrate some data to it and re-purpose the one that protrudes.

Jaglover wrote:
Using hard links as rsnapshot does you can have 100 backups taking up only a little more than one single backup.
I need to look into how that works. It's a losing battle, but I try to not add more things onto my system that rely on dynamic languages.

Jaglover wrote:
You can use two or more USB flash drives to get better protection than RAID-1 while it takes less space, less energy and costs less.
I haven't priced 1TB flash drives, but last I looked, they were pricier than I perceived their value. But as I mentioned, I'm not current on whether or not their reliability has improved. Certainly they might be nice as a third option. I could probably use them only for "personal" data instead of complete system data.

Jaglover wrote:
Just add here whatever your creativity can produce ...
... within available time and financial constraints ;). I've ignored a "good" solution for a long time. This is my first pass at a "real" solution. I'll adjust it where it is needed.
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PostPosted: Tue Jun 15, 2021 4:03 am    Post subject: Reply with quote

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.
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PostPosted: Tue Jun 15, 2021 9:20 pm    Post subject: Reply with quote

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
Code:
fractal /usr/src/linux # lsblk
NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sda      8:0    0  1.8T  0 disk
├─sda1   8:1    0  256M  0 part /boot
├─sda2   8:2    0   64G  0 part [SWAP]
└─sda3   8:3    0  1.8T  0 part /
sdb      8:16   0  3.6T  0 disk
sdc      8:32   0  3.6T  0 disk


So i tried using fdisk to label them (GPT) and create Linux swap partitions... but still no joy. Have since deleted them, but now get
fractal /usr/src/linux # mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/sdb1 /dev/sdc1
mdadm: cannot open /dev/sdb1: Device or resource busy


Is that page maybe missing a step ?

FWIW, this box only shows lvm in rc-update, no mdadm, So I must have followed a different process last time ...


Thoroughly stuck :-)

Thanks, ian

code tags added by NeddySeagoon
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PostPosted: Tue Jun 15, 2021 9:55 pm    Post subject: Reply with quote

iandoug,

Code:
fractal /usr/src/linux # lsblk
NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sdb      8:16   0  3.6T  0 disk
sdc      8:32   0  3.6T  0 disk


There are no partitions there so
Code:
mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/sdb1 /dev/sdc1
will fail.
Neither /dev/sdb1 nor /dev/sdc1 exist.
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PostPosted: Wed Jun 16, 2021 7:45 am    Post subject: Reply with quote

NeddySeagoon wrote:
iandoug,


There are no partitions there so
Code:
mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/sdb1 /dev/sdc1
will fail.
Neither /dev/sdb1 nor /dev/sdc1 exist.



I tried again...

Code:

fractal /home/ian # fdisk /dev/sdb

Welcome to fdisk (util-linux 2.36.2).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.


Command (m for help): p
Disk /dev/sdb: 3.64 TiB, 4000787030016 bytes, 7814037168 sectors
Disk model: WDC WD4005FZBX-0
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: gpt
Disk identifier: 05E64D31-1408-B245-B3B1-8C832B53787A

Device     Start        End    Sectors  Size Type
/dev/sdb1   2048 7814037134 7814035087  3.6T Linux RAID


fractal /home/ian # fdisk /dev/sdc

Welcome to fdisk (util-linux 2.36.2).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.


Command (m for help): p
Disk /dev/sdc: 3.64 TiB, 4000787030016 bytes, 7814037168 sectors
Disk model: WDC WD4005FZBX-0
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: gpt
Disk identifier: ED82EF54-4736-E34A-B07E-CF872FAC41C0

Device     Start        End    Sectors  Size Type
/dev/sdc1   2048 7814037134 7814035087  3.6T Linux RAID


fractal /home/ian # mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/sdb1 /dev/sdc1
mdadm: cannot open /dev/sdb1: Device or resource busy





Maybe I need to reboot and try again. Will be later.

Thanks, Ian
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PostPosted: Wed Jun 16, 2021 7:20 pm    Post subject: Reply with quote

Appears correct now ...

Code:

fractal /home/ian #  mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/sdb1 /dev/sdc1
mdadm: partition table exists on /dev/sdb1
mdadm: partition table exists on /dev/sdb1 but will be lost or
       meaningless after creating array
mdadm: Note: this array has metadata at the start and
    may not be suitable as a boot device.  If you plan to
    store '/boot' on this device please ensure that
    your boot-loader understands md/v1.x metadata, or use
    --metadata=0.90
Continue creating array? y
mdadm: Defaulting to version 1.2 metadata
mdadm: array /dev/md0 started.
fractal /home/ian # lsblk
NAME    MAJ:MIN RM  SIZE RO TYPE  MOUNTPOINT
sda       8:0    0  1.8T  0 disk 
├─sda1    8:1    0  256M  0 part  /boot
├─sda2    8:2    0   64G  0 part  [SWAP]
└─sda3    8:3    0  1.8T  0 part  /
sdb       8:16   0  3.6T  0 disk 
└─sdb1    8:17   0  3.6T  0 part 
  └─md0   9:0    0  3.6T  0 raid1
sdc       8:32   0  3.6T  0 disk 
└─sdc1    8:33   0  3.6T  0 part 
  └─md0   9:0    0  3.6T  0 raid1


Now to migrate /home there ... should have done this before creating a user...

Thanks, Ian
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