Guidance Building Up my Mint PC

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Dark Owl
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Re: Guidance Building Up my Mint PC

Post by Dark Owl »

Kadaitcha Man wrote:
Fri Jul 03, 2020 8:21 pm
Also, you won't get all that much of a performance boost out of putting just /home on RAID. To get the benefit, you need the OS on RAID.
It's not about performance, it's about data security by instantaneous backup (hence RAID 1).

I'm not a commercial organisation with critical data, I don't need gold-standard backup procedures, and life gets in the way of routine housekeeping... so defending against HDD failure using a mirror drive seems like the way to go for me.

Back in IDE days I had an AMD486 motherboard which did hardware RAID and even fooled Windows into thinking it was just a disk. I was very disappointed when I discovered my current mobo RAID support is essentially through drivers, so I ditched that idea and got to grips with mdadm. Any hardware RAID adapter cards I could find looked expensive, but I'm happy to follow up your suggestion.

If I can put the RAID at the hardware level, that's one less thing for the OS to get in the way of, but something to ponder: from what I've seen so far, the RAID drives under mdadm are pretty safe from a raw Mint installation without mdadm installed, and then installing mdadm makes the existing RAID drives available again. That seems pretty robust. If the hardware RAID card failed, it would have to be replaced.

A nice feature of the AMD486 hardware RAID was that each drive was just "normal" - if the PC went dead, either drive would work directly on another PC without special measures. Is that the same with your 6805T?

Update: £24 + delivery, that's OK. If I saw it before I would have not understood "SAS".

Note to self: http://download.adaptec.com/pdfs/user_g ... 2_2011.pdf
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Kadaitcha Man
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Re: Guidance Building Up my Mint PC

Post by Kadaitcha Man »

Dark Owl wrote:
Sat Jul 04, 2020 2:40 am
A nice feature of the AMD486 hardware RAID was that each drive was just "normal" - if the PC went dead, either drive would work directly on another PC without special measures. Is that the same with your 6805T?
Yes, just pull it out, with the cables and disks labelled, and plug it into a different machine.

I get what you're saying about not being commercial, but for 25 quid you've got far better protection of your data than you would have with software RAID, and it's far easier to extend. I'm not commercial, but I have an extensive video library so I have two backup servers and both servers have 7 disks coming off a 6805T. I wouldn't trust software RAID for that.
... from what I've seen so far, the RAID drives under mdadm are pretty safe from a raw Mint installation without mdadm installed...
Well, it's your data. It only takes one brown-out to kill software RAID. Been there, done that.
If the hardware RAID card failed, it would have to be replaced.
Yes, but surely they're cheap enough to keep a spare around. Anyway, it's not my job to convince you, only to give you options. At the end of the day, it's your call about the risk you take with software RAID and no hardware backup.
It's pronounced kad-eye-cha, not kada-itcha.
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Re: Guidance Building Up my Mint PC

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Kadaitcha Man wrote:
Sat Jul 04, 2020 3:26 am
Yes, just pull it out, with the cables and disks labelled, and plug it into a different machine.
That's not as nice as if one drive (from a mirror) can stand on its own (as did mine from the 486). I've looked at the 6805 PDF, and I see it still needs drivers. I don't understand why a RAID array doesn't look like a normal drive to the OS, with the controller hardware looking after all the translation invisibly.

In the case of a mirror: all the controller has to do is duplicate the write to another drive, and in the case of read compare the two fetches and if one of them fails send the good one. Granted it's not so simple for other configurations, but it still need not concern the OS that it's talking to the disk through a RAID controller instead of a standard controller.
Kadaitcha Man wrote:
Sat Jul 04, 2020 3:26 am
it's not my job to convince you, only to give you options.
Absolutely. Too many people fail to understand forums are for reasoned debate and exchanging opinions, and get annoyed if anyone disagrees. There is rarely a "one fits all" solution.
Last edited by Dark Owl on Sat Jul 04, 2020 4:44 am, edited 1 time in total.
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Re: Guidance Building Up my Mint PC

Post by Kadaitcha Man »

Dark Owl wrote:
Sat Jul 04, 2020 4:40 am
I see it still needs drivers.
I already told you, explicitly, that it works out of the box ... "With this setup there is absolutely no wrangling, it all works out of the box."

Yes, it needs drivers, and the kernel provides those drivers OOtB.
I don't understand why a RAID array doesn't look like a normal drive to the OS
I don't understand where that idea comes from. Once the array is set up, it looks like a normal drive to Linux.
It's pronounced kad-eye-cha, not kada-itcha.
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Re: Guidance Building Up my Mint PC

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Kadaitcha Man wrote:
Sat Jul 04, 2020 4:43 am
I already told you, explicitly, that it works out of the box...

I don't understand where that idea comes from. Once the array is set up, it looks like a normal drive to Linux.
I think we might be talking at cross-purposes. You are (I think) looking purely at the practical level, but I cogitate on a philosophical level (which often has to defer to pragmatism).

"Once the array is set up, it looks like a normal drive to Linux" - does that mean Linux can't tell that it is accessing a RAID rather than a standard drive? That's what I would mean by transparent.

Practical question: what does a drive initialised through the 6805T look like if it were connected direct (without the 6805T)?
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Re: Guidance Building Up my Mint PC

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Kadaitcha Man wrote:
Sat Jul 04, 2020 3:26 am
It only takes one brown-out to kill software RAID. Been there, done that.
I can tell a better one: (486) I had a mains power surge which resulted in a spike in the 12V rail out of my PSU. That knocked out the motor control on both my mirror drives. I figured I might recover one by buying another drive of the same model and transplanting the controller board, but although the model was the same, the exact build wasn't and the controllers wouldn't swap.

However, the motor control chip was the same. I transplanted it from the new board to an old board, and got the drive running long enough to pull the data. I wasn't able to resolder the thermal bonds under the package, so it burnt out soon after that.

Since then I've had a power-conditioning UPS behind my PC!
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Re: Guidance Building Up my Mint PC

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Dark Owl wrote:
Sat Jul 04, 2020 4:53 am
"Once the array is set up, it looks like a normal drive to Linux" - does that mean Linux can't tell that it is accessing a RAID rather than a standard drive? That's what I would mean by transparent.
For all intents and purposes, the linux kernel treats all block devices the same, be they USB HDD, USB flash, microSD, hardware RAID, software RAID, SATA, NVMe, PATA or whatever else there may be out there.
Practical question: what does a drive initialised through the 6805T look like if it were connected direct (without the 6805T)?
That will depend on the RAID type. A RAID1 disk will look like a disk with data on it, but a RAID0, RAID50, RAID5EE, RAID10 disk et al will look unformatted. That would not change with software RAID.

Code: Select all

kman@X570:~$ lsblk
NAME        MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
sda           8:0    1  10.9T  0 disk 
└─sda1        8:1    1  10.9T  0 part /media/boot/SERVER 
nvme0n1     259:0    0 238.5G  0 disk 
├─nvme0n1p1 259:1    0 185.6G  0 part /home
└─nvme0n1p2 259:2    0  39.3G  0 part /

Code: Select all

kman@X570:~$ sudo blkid
/dev/sda1: LABEL="SERVER" UUID="38101b12-740c-49e9-bd1d-6dbaa6262f2d" TYPE="ext4" PARTUUID="2caf08f7-0bc4-3943-bb2e-459802b14923"
/dev/nvme0n1: PTUUID="1bf1ba2e" PTTYPE="dos"
/dev/nvme0n1p1: LABEL="Home" UUID="ba01ce4d-7888-482b-89e3-877ec213c723" TYPE="ext4" PARTUUID="1bf1ba2e-01"
/dev/nvme0n1p2: LABEL="System" UUID="83c28f12-4de3-4a41-b862-656a0b78ed12" TYPE="ext4" PARTUUID="1bf1ba2e-02"
sda1 is seen by the kernel as simply a 12TB block device. The card has 7 drives, one of the drives is a hot spare. Linux simply sees the block device presented by the card, just as it sees all other block devices. It doesn't care what's behind the block device and it doesn't need to know.

This is what inxi sees:

Code: Select all

Drives:    HDD Total Size: 12359.1GB (71.8% used)
ID-1: /dev/sda model: RAID50 size: 11983.0GB temp: 0C
ID-2: /dev/nvme0n1 model: XPG_SPECTRIX_S40G size: 256.1GB
RAID:      No RAID devices: /proc/mdstat, md_mod kernel module present
Note that when queried, the card reports to inxi that the device is a model RAID50. The last line reports No RAID devices but that is referring to software RAID.

As an administrator of a hardware RAID 6805T, you can install the MAXview web server to look at what the card sees:
Screenshot_20200704_203252.jpg
So, what the card sees and what the linux kernel sees are two different things.
It's pronounced kad-eye-cha, not kada-itcha.
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Re: Guidance Building Up my Mint PC

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Kadaitcha Man wrote:
Sat Jul 04, 2020 6:54 am
A RAID1 disk will look like a disk with data on it
That's what I've been trying to drill down to, thanks.
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Re: Guidance Building Up my Mint PC

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Kadaitcha Man wrote:
Fri Jul 03, 2020 8:21 pm
I would recommend spending 40 or so US dollars on a hardware RAID card such as the Adaptec 6805T
I can't find a sensible 6805T to buy - would a 5405 do?

https://www.techbuyer.com/tca-00275-04- ... er-122212/
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Re: Guidance Building Up my Mint PC

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Dark Owl wrote:
Sun Jul 19, 2020 12:53 pm
Kadaitcha Man wrote:
Fri Jul 03, 2020 8:21 pm
I would recommend spending 40 or so US dollars on a hardware RAID card such as the Adaptec 6805T
I can't find a sensible 6805T to buy - would a 5405 do?

https://www.techbuyer.com/tca-00275-04- ... er-122212/
Yes, from the small amount of reading I did, it uses the same kernel driver, aacraid. It should just plug into a PCIe slot and that's all that's needed to bring it up under Linux. Of course, you would have to enter its BIOS to set up the RAID, but Linux will see the card out of the box. The 5405 appears to be exactly half a 6805. The only thing you would need is the correct cable to get to convert it to support SATA drives. You need SFF-8087 Mini SAS to SATA.

I normally buy my Adaptec cards from China, off ebay. They seem to be cheaper.
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Re: Guidance Building Up my Mint PC

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Kadaitcha Man wrote:
Sun Jul 19, 2020 7:02 pm
I normally buy my Adaptec cards from China, off ebay. They seem to be cheaper.
I made my principles turn their backs for a minute and did (a 6805, with battery pack although I'm not sure I'll use it just for mirror RAID). Estimated delivery was 3-18 Aug. It turned up today (27th July)!

Just waiting for the SAS adapter cable now...
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Re: Guidance Building Up my Mint PC

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Dark Owl wrote:
Mon Jul 27, 2020 9:25 am
I made my principles turn their backs for a minute and did (a 6805, with battery pack although I'm not sure I'll use it just for mirror RAID). Estimated delivery was 3-18 Aug. It turned up today (27th July)!

Just waiting for the SAS adapter cable now...
You won't be sorry :)
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Re: Guidance Building Up my Mint PC

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Kadaitcha Man wrote:
Mon Jul 27, 2020 6:33 pm
You won't be sorry
It's in and running. I reinstalled LM20 from scratch, taking advantage of the install options to put boot and root on SSD, temp and swap on a 500GB stand-alone drive, home on one 1.3TB RAID mirror, and another 1.8TB RAID mirror uncommitted at this time.

Definitely a lot easier than mucking about with mdadm and trying to get it recognised at boot time.

The main annoyance now is that the RAID controller bios adds 40s to my boot time.
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Re: Guidance Building Up my Mint PC

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Dark Owl wrote:
Fri Jul 03, 2020 5:57 pm
Why can't the whole /home tree (all users) be declared/redirected onto another partition/drive?
The answer is that it can, and the easiest way to set this up is during installation by taking the "something else" option.
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Re: Guidance Building Up my Mint PC

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Removing one disk for use on another machine is good. I used to do that with Windows server to replicate server system disks across hundreds of servers. Then Microsoft changed their RAID to stop that working. I found the same problem with Linux RAID and a variety of hardware RAID devices.

How long does it take to recover from a disk failure? Using some top of the line hardware RAID devices under $1000, the devices used from 14 hours upwards to replicate one disk to the other. It was faster to backup to an external disk, wipe the RAID array, then restore the files. How long does the Adaptec device take per terabyte?
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Re: Guidance Building Up my Mint PC

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Petermint wrote:
Fri Aug 07, 2020 9:20 pm
How long does the Adaptec device take per terabyte?
Don't know, don't care, won't find out until I need to do it. Neither is my OS on the RAID (although backup snapshots might be).

You can check the specs yourself: http://download.adaptec.com/pdfs/user_g ... 2_2011.pdf
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