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After much messing about with software RAID 5 with FreeNAS I have given up. I'm not finding it's a solution I feel my data is safe with. This could be down to the fact I am still a total Linux/BSD noob, but FreeNAS also seems to be locking up my system quite a bit so I don't think it's all my fault

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I'm curious if it's the lockups or your desire for 'safety' that has steered you away from software RAID5.

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If it's the lockups, the specs you quote are WAY above what I built for my NAS box, so something's wrong with your software selection or maybe execution.

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If it's 'data safety', I'm wondering what specific points have you found to convince you hardware RAID is the way to go.

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I figure a hardware solution will be more able to recover from a drive failure.

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but there's more chance of losing everything too.

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I have several *very* high-end "hardware" RAID boxes here, and all of them use Linux software RAID internally.

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but there's more chance of losing everything too.

How come?

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Oh yea, big problem there, esp if I use a 2nd hand eBay card.

Well, now I am totally confused. I don't want to spend much more money on this, can anyone recommend a Linux disro I may get on with ???

Cheers

Cris.

Well, totally sight-unseen, I would recommend Ubuntu Server. The new "Fiesty" is due for final (initial) release later this month, and would probably do an excellent job for you.

(I don't currently have any RAIDs set up around here; the big iron bits I just do manually, because I'm working at a layer or two beneath the RAID s/w. In other words, I'm not much use to you unless you can pop over with your system for an evening. )

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I'm not much use to you unless you can pop over with your system for an evening.

Great! I'll be on the 20:00, see you in 12 hours!

Now do you think I can check in a 4U Rackmount case as hand baggage....

On the more serious note, I will give your suggestion a try and see how I get on.

Cheers

Cris.

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I will give your suggestion a try and see how I get on.

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Two of my biggest problems with (???) are that ...

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... it regularly completely revamps large subsystems

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.. and its documentation is for shit.

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that doesn't mean that Linux doesn't change stuff out with little ramification.

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They might decide to swap out the RAID system tomorrow with a completely new interface

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Why not just go RAID1 or use a large usb drive to backup your data?

All good points! The basic idea was to create something cheap (ie using as many parts as I already have) and something that offers as near to 100% up time of data 24/7 as possible with DIY kit.

I am very very lazy when it comes to backups, I want a NAS to sit on my network to take regular automated backups from my 4 main systems in the house. A USB drive is out of the question. The HD's in this system have been taken from various other ideas for back up involving USB solutions.

As for RAID 5, I guess it looked really good on the box in effect giving me 50% extra space from 4 drives. I thought it would be easy, as I have found other RAID solutions in the past. I am starting to wonder if I should start looking at the other solutions again, but it has to sit on the network.

FreeNAS has been a bit of a disapointment, it looks really good, says it does everything I want it to, but it's not very stable yet. I think I will go with Mark's suggestion as this was also used in an article I linked to further up in the thread. I also may try clarkconnect as I am confident with that.

One thing I really wanted was a system that would boot from a USB stick. FreeNAS does this really well. Power consumption is quite important for me, and the idea of not having HD's spun up until really needed sounds like a good idea to me. Heat is an ongoing issue with my under stairs server room, which seems to be stable at the moment, but I think 5 HD's spun up will tip that balance

Cheers

Cris.

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FreeNAS has been a bit of a disapointment, it looks really good, says it does everything I want it to, but it's not very stable yet.

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Could there be a hardware problem?

I don't think so.

The lock ups are pretty consistant. For example, once the RAID 5 is complete, it locks when you hit the format button, every time! I have tried different RAM, but when I pulled them out I noticed the originals were Crucial, and that this MD and CPU were my CCTV server for about a year, in this case. Never crashed once, which is pretty amazing for XP I think.

I can bring it over on Sunday if you want to take a look for me

Cheers

Cris.

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f there was a better term for what I was talking about, I'd have used it.

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Well, my usual example is the NAT/FW code. How many times has that been swapped out over the years? Three? Each incompatible with the previous.

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How many attempts at a /dev filesystem have there been?

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How often did that break existing things?

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Glibc incompatibilites have abounded.

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Gcc problems.

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The list goes on and on.

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How many attempts at a /dev filesystem have there been?

The original "static /dev" from 1991 is still supported and works fine. Over the past two years, various new features in the kernel have enabled proper hotplug support, and a userspace "udev" device manager app has grown up to use those features. But again, the original 1991 method still works just fine.

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How often did that break existing things?

Zero, or near to it, unless one deliberatly switched to a different method.
Installing an entire new system, eg. Ubuntu, of course will give the new methods as default. As it should.

As a matter of fact, because I installed my machines a *looong* time ago and just slowly upgraded, swapping out graphics, RAM, CPUs, motherboards, hard disks etc over time (no 'activation' here) I only moved to udev last week.
I think I wanted better device naming for my USB memory stick.
Everything else just worked the same
I just typed:
apt-get install udev
and there it was (no reboot FWIW, just a completely different way of accessing hardware online at once).
This is under Debian though - none of this flash Ubuntu nonsense

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The list goes on and on.

It certainly does! Stellar backward compatibility, no major upheavals in established distros. The hot new ones like (K)Ubuntu of course install only the latest stuff by default, but the older stuff is there too.

I installed Redhat 4.1 (I think) on an AMD something machine a while back (1997). Then I upgraded to Redhat 7.2 when it came out. in 2002-ish Then, since it worked, I left it serving my emails. I upgraded the kernel along the way for various reasons - it became a firewall so I suspect I did the ipxxxx things. I'm sure a lot of the code was the same as I ran in '96 - it certainly was running the same 1992 1Gb SCSI disks I liberated from the skip at SGI when I retired it. It's still in the spare room for sentimental reasons.

Also, just before I retired it, since it had an ISA motherboard I dug out an old 10Mb hard disk that I used in college on an Amstrad 2086 in about 1992-ish. It was MFM and used RLE (I think). Compiled the kernel, plugged it in and read my data.

Couldn't run the turbo-pascal - though I daresay I could have loaded an emulator and installed something...

And, as for the gcc thing - last week was yet another first for me
My first empeg kernel compile on my 2.6.18.3 (old, I know) *Intel based* kernel.
I just downloaded the 2.95 arm cross compile toolchain built on god-knows what system back in the mists of time and ran it and got a new kernel.

I wonder if the same proprietary toolchain used in Cambridge back in the day would run under Vista?
I can't remember why the player code is now totally dead but isn't it because the toolchain won't run? (really, I don't know but I thought that was the reason).

Feel free to moan about suspend/hibernate though
Or 3D-acceleration on graphics cards.
or many many other things - what's life without tribes?

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mdadm --force is a scary thing to use late at night trying to recover the array.

Yep - been there...

One of my motivations for the wiki was to try and gather best-practices to explain what you should do in this situation.

Oh, and 'this situation" is usually a catastrophic failure where you've lost multiple drives at once or in a cascade. Your array is dead, dead, dead. You have blown the redundancy you designed in (ie you lost 3+ drives in a RAID6 array).

You have however done data-recovery using ddrescue and friends and there is a chance that you can recover something - try *that* on a hardware raid

I think I'm right in saying that if you use --force it will recreate your superblocks and not touch your data.
If you get it wrong you re-run it with different parameters until it works.

**BUT**
If, for some reason the kernel thinks that your array needs 'synchronising' then it will start writing all over your data and 'goodnight Vienna'.
So it's a good idea to use --force with the 'missing' keyword to assemble the array in 'degraded' mode. That way you can try a read-only mount and see if there is anything resembling a filesystem there...

This kind of stuff is what I want to put up on the wiki after running it by the list.

The linux-raid list (http://vger.kernel.org/majordomo-info.html) is a very friendly and helpful place BTW - far less busy than lkml and much more newbie-friendly - do pop in if you have any raid or recovery questions...


PS My favourite HW raid issues: when your raid card goes titsup - how much are they? Do they even make those Adaptec raid cards you bought 4 years ago? Are the new ones compatible? What happens if you can't get a disk that's *exactly* the same anymore?

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PS My favourite HW raid issues: when your raid card goes titsup - how much are they? Do they even make those Adaptec raid cards you bought 4 years ago? Are the new ones compatible? What happens if you can't get a disk that's *exactly* the same anymore?

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I wonder if the same proprietary toolchain used in Cambridge back in the day would run under Vista?
I can't remember why the player code is now totally dead but isn't it because the toolchain won't run? (really, I don't know but I thought that was the reason).

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I could be wrong, but as far as I know there was no such proprietary toolchain. The empeg player code is C/C++ code that runs on Linux, I have always assumed that it was also built on Linux using the standard toolchain.

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compiled with Visual C++ 6, which does still run on Vista, so ner.

to you too

(at last, a proper debate!)

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I will give your suggestion a try and see how I get on.

Ack. I'm pulling down the current daily build of "Fiesty Server" to try on one of the racks here later today or tomorrow. If I remember, I'll report back on how it looks for RAID stuff.

Cheers

I'm building the Ubuntu Feisty system right now using yesterday's image of the "alternate" installer CD. So far, so good. I found this set of instructions that I'm using as a loose guide for this:

http://www.debian-administration.org/articles/512

There are a few things I'm trying differently, and we'll see how those work out.

My oh my, it certainly does take some time to construct a 3TB RAID5 array from scratch..

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My oh my, it certainly does take some time to construct a 3TB RAID5 array from scratch..

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My oh my, it certainly does take some time to construct a 3TB RAID5 array from scratch..

Seriously?
Or do you mean the whole system rather than just the array?

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Just the array -- it does it in the background, of course, but the initial sync involves rewriting the entire contents of the entire space of the entire array. That takes a while with 3TB of disk space.

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But I'm redoing it again now -- my experiment didn't pan out, and smaller physical RAID partitions will make testing failure modes a lot less time consuming later on.

So this time, the RAID5 will be only 120GB instead of 3TB.

don't forget bitmaps.

Resyncing a dirty Tb array takes seconds

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Why, though? Can't it just treat the sector contents as undefined until written to? Why isn't setup of an empty array instantaneous?

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There is an --assume-clean option which is safe for raid1 and raid6 but for raid5 it is NOT safe to skip the initial sync.

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For raid6 it is also safe to not sync first, though with the same caveat as raid1. Raid6 always updates parity by reading all blocks in the stripe that aren't known and calculating P and Q. So the first write to a stripe will make P and Q correct for that stripe. This is current behaviour. I don't think I can guarantee it will never changed.

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Why, though? Can't it just treat the sector contents as undefined until written to? Why isn't setup of an empty array instantaneous?

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Just because I'm interested.... could you use the array whilst this was going on?

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But I'm redoing it again now -- my experiment didn't pan out

Well that makes me feel a whole lot better

If you have problems it must be nearly impossible for me to do it!

Amazingly I got a knock on my door about an hour ago, it was the postman. I bid on one of the LSI cards the otherday and it's turned up already! £35 (US$65 ?) no bad!

Within the hour I have FreeNAS running, RAID5 working and the box sat on my network taking files. Certainly pain free to this point. I haven't however figured out how to tell the array is healthy to start with, and of course haven't tested it yet for drive failure/recovery.

On thing I have noticed is speed, so far this seems to be much slower than the software solution, but maybe this is because the array is still building in the background, the drive are certainly running, or maybe the card won't let them power down?

I still want to try the software approach due to some of the arguments put forward in the thread, I just need a slightly less painful experience.

Cheers

Cris.

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and of course haven't tested it yet for drive failure/recovery

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But I'm redoing it again now -- my experiment didn't pan out

Well that makes me feel a whole lot better

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But I'm redoing it again now -- my experiment didn't pan out

Well that makes me feel a whole lot better

Heh.. I just didn't follow the directions given -- tried something different (yet similar..) and it failed to boot after the install. Got distracted with another project afterwards, so I'll try it again today sometime.

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I'll try pulling/reinserting drives next.

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I could of course just drop back to a simple mirror and forget RAID5, but I really want that extra 250Gb.

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I could of course just drop back to a simple mirror and forget RAID5, but I really want that extra 250Gb.

Yeah, I know the feeling.

A *lot* of people seem to prefer RAID 1+0 with a four drive setup.
That's two pairs of RAID1, which are then combined into a single virtual drive
with RAID0 striping across the two pairs. Or the other way around (0+1)

Very reliable, very fast -- more so than just two pairs of RAID1 would be.
But still no extra 250GB.

Cheers

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Wow! Thanks Mark!

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A *lot* of people seem to prefer RAID 1+0 .... Or the other way around (0+1)

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Wow! Thanks Mark!

Well, on a related note: the Feisty bug database is presently littered with RAID roadkill. Lots of people seem to have seen similar installer issues to what I ran into, and my fix for it (intervene in the boot process to get it up, and then just update the packages to repair it all) doesn't work for most of them.

Okay, the latest word on this is that those fixes have now made it into the installer disks as of 14-April-2007, and RAID installs now seem to be working for everyone.

Woo-Hoo!

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But still no extra 250GB

In an ideal world I would just go out any buy 4 x 500Gb SATA drives, a local supplier has Seagate drives at under £70 now. With this solution 1Tb would be more than enough so RAID10 would be the perfect solution.

Although speed isn't a major issue at present, I'm running and ever increasing Gigabit network at home. At the moment it's just the Macbook and one of the servers as my switch only has 2 Gigabit ports. I have noticed that even though the spec of the new NAS box is much higher than my current clarkconnect firewall, the CC box transfers are much quicker. This could be down to the intel gigabit nic I suppose, the one in the NAS is a £15 D-Link (nasty!).

If only I had put a bet on Ascot I could be straight down to pick up my SATA drives

Cheers

Cris.

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Okay, the latest word on this is that those fixes have now made it into the installer disks as of 14-April-2007, and RAID installs now seem to be working for everyone.

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I do have enough spare HD's to run 4 x 250Gb and 3 x 120Gb arrays

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Am I right in assuming I can't boot from RAID5? Or could I do a complex setup of striping and mirroring a 1Gb partition and then RAID5 the rest? Putting a 5th drive in the system isn't something I really want to do at this stage if I can help it.

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The standard way is to have a smallish RAID1 partition for /boot (or the rootfs), and a RAID5 partition for the rest. On each drive. Just like in the article I linked earlier.

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With the two O/S partitions, you can experiment with a newer O/S version in the future, and yet still have your original working O/S version intact until all is well with the new one.

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Oh, one tip if you go software side. Don't RAID the hard disk. Create partitions on the disks and RAID those, making the partition a bit smaller then the hard disk. That way, if one of your Brand X 120gig drives fails, and only a Brand Y 120g can be found later. There is a possibility Brand Y 120 gig will be a smidge smaller then Brand X, and by using a smaller setup of space on the old disk, the new one should still work into the array.

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My problem is that I'm not a Linux god.

Me too!

I have only had the chance to test the MegaRAID i4 once so far. What I did notice is that if you reboot it does start the rebuild right from the start again. ie if you were at 5% and need to reboot your machine for some reason, when it all comes back up the MegaRAID starts again from 0%, but I did find it started again automatically.

I'm really glad I hve given "hardware" RAID a try. I can now really see Mark's point, you do stand more of a chance of getting your data back with software RAID if you know what you are doing.

My problem is I don't know what I am doing, yet

The other problem with the MegaRAID i4 is that it keeps the disc spun up 100% I left the system on over the weekend while I was away from home, nobody as been using the NAS and the drives are a full temp. For this reason alone the i4 is going back on eBay. This can't be good for the type of drive I am using here!

Cheers

Cris.

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suppose there are some new updates to the RAID implementation and I end up screwing up my data. Maybe I just don't choose the right compile flags to ensure compatibility or something like that.

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Also what if I have a catastrophic hardware failure (fried motherboard or something) and have to rebuild everything. I KNOW that it is possible to rebuild everything to get the data off the drives, but maybe I'm not capable of doing it without making a mistake somewhere along the way.

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My problem is that I'm not a Linux god.

I'm really glad I hve given "hardware" RAID a try. I can now really see Mark's point, you do stand more of a chance of getting your data back with software RAID if you know what you are doing.

My problem is I don't know what I am doing, yet

That's the thing about 'community'

The linux-raid list has regular 'help' emails and they almost all get sorted - I think the only caveat is "don't mess if you don't know what you're doing - just ask".

Also, you mentioned wanting to power down the disks in your raid. I'm not sure how well that works 'out of the box' under linux. You may need to do some fiddling.

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I'm not throwing out FUD

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I see posts about using the force flag and various "pucker" factors in this thread and hence some of my fears. I figure plugging the array into the new box would require forcing it online.

That's the problem with being fully honest - I did try to emphasise that the --force stuff was to do recovery in situations where you were already royally FUBARed.

Let me put it this way, if and only if your system burns to the ground and is eaten by ants then linux raid *may* need to use the --force command Better?

Moving to another machine - business as usual.
Disk failure - business as usual.
Switch from RedHat to SUSE to Debian - business as usual.
Upgrade kernel - business as usual.
etc etc

One of my biggest problems with linux RAID way back when was when a disk failed and I didn't notice for months - the thing just kept going.

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Also, you mentioned wanting to power down the disks in your raid. I'm not sure how well that works 'out of the box' under linux. You may need to do some fiddling.

In FreeNAS it was one feature that worked really well, it must cache part/all of the file table (or whatever?) as you could pretty much browse the NAS and the drives spun up when a file was requested, but I never did get to the point of mave many files on it.

The only slight problem was that the WD drive sins up much slower than the seagate driver, that wa causing some retry errors in the log files, but from my point of view it worked pretty well.

I think the Software RAID argument is winning the battle at the moment, like you said if I get stuck all I need to do is ask

Cheers

Cris.

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I'm not throwing out FUD

Just trying to prevent it from being interpreted as such when somebody stumbles over this thread via Google.

You actually sound to me like a pretty competent user of this stuff -- more power to ya!

Cheers

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Periodic backups, there is no substitute.

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Considering Linux as a software RAID solution, I wonder how many people in the world have intimate knowledge of Linux on a par with some of the contributors of this forum? I’ll bet not many. This is the reason why software RAID5 is not an option for me. Some of you make it sound so easy just to do whatever needs to be done to fix whatever problems might occur.

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Again, the issues with administrating a RAID array are not unique to Linux. RAID5 failures will likely be just as complex to recover from regardless of the underlying O/S, or whether it's "hardware" or "software" RAID.

Just trying to keep things clear here for posterity (aka. "google").

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When I was using RAID5 it was the total repository of all of my media. There was no other backup. At the time I considered RAID5 to be sufficient unto itself. This was a mistake. How are you planning on monitoring the status of your drives? I used the Promise Superswap 1000 drive bays that gave constant condition status via LED’s. Even with this I lost my data once. You think it’s a hassle copying 700GB? How about re-ripping a TB? I guess I have been burned too many times. What I purpose is probably extreme.

There's a lot being said here; some is linux specific but most, I think, is generic.

Clearly if you are experienced in one OS and move to another then there's a learning curve - that said:

Setting up:
Linux RAID is simple and generally just works.
BIOS or windows RAID is probably a touch simpler and generally just works.
Not much in it.

Monitoring:
Linux RAID is simple and generally just works via email. [My machines talk to me if a disk fails.]
BIOS or windows RAID may use email, LEDs, beep or just notify you on reboot (not good for a server) .
Not much in it.

Disaster:
For an average user it is feasible to recover a Linux RAID systems when things go badly wrong (and I'm talking about massive hardware failure here!) but it needs to be dug into very deeply and can become very complex indeed. [However a few hours of hair pulling may be a lot easier than a 1Tb restore!]

For an average user if you have an unexpected hardware failure with windows or BIOS RAID then you are screwed. You would need to spend real cash (many hundreds of $) with a forensic data recovery firm to stand a chance of getting your data back - or just start restoring.

Huge difference.


Another problem area is how people thing about risk, backups and resilience.

In other words : do I bother with RAID or do I just have backups.

It's complex; but in general RAID reduces the likelihood of needing to restore from backups - Neutrino you are 100% spot on when you say it is not sufficient to replace backups. However it does almost eliminate the need to restore from backups for disk failures.

That's worth restating:
* I'll (almost) never need to restore from backup due to disk failure.

Here, I think the problem you will face Neutrino is that you are almost *certain* to lose all your data and have to restore from backup. (I assume you have 1Tb of data on 3x320Gb disks = no resilience). Your system is 3 times more fragile than a single disk system. Assuming drives are 95% likely to die in 6 years (even spread) then your system is 95% likely to die within 2 years - I hope you have an OCD tendency to backup!



FWIW I have multiple data stores.
One is for music and films that I have recorded or ripped. The backup is the original media. When (not if) a drive fails, I just replace it. I doubt I will ever have to re-rip. If I didn't have a resilient setup then I'd have to re-rip (or restore) every time a drive failed.

Another store is a simple striped array.
I hold important data on there and it backs up incrementally onto a separate striped array using snapshots.
Having the backup online all the time means I can monitor the health and replace drives.


I hope this comes across in the spirit it's intended

A few years ago I had a disk failure on the disk with all my photos on it.
I bought a replacement hard disk and did a disk copy from my backup to my new disk.
Sadly I swapped the device names and overwrote my backup with a blank disk. I felt a horrible cold chill and the hairs on the back of my neck stood up as I realised that I'd lost years worth of photos.
Luckily I was a sysadmin at the time and by 'habit', as soon as the disk failed I made a copy of the backup to some free space. It took me 10 seconds to remember that I had the copy - they were not pleasant seconds.
I did however just do a quick 'copy' and the timestamps on all those files show the date and time of the near-disaster.

So the reason I bother with this RAID stuff is because I really worry about the 'normal' people who are going to lose their digital memories and I try to help out
I would like to see Linux RAID get a nicer frontend (for home use) and better disaster recovery etc - it will happen.

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So the reason I bother with this RAID stuff is because I really worry about the 'normal' people who are going to lose their digital memories and I try to help out

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So the reason I bother with this RAID stuff is because I really worry about the 'normal' people who are going to lose their digital memories and I try to help out

And I was agreeing with your post until I read that.
...
I'll get off my soap box now. But I won't hesitate to get back on it if someone starts implying raid is a backup solution.

Matthew
PS: Perhaps I'm reading your post wrong, and you mean preserving memories is the reason you help other people with their RAID recovery. I still stand by my rant about backups, even if it doesn't apply to you.

You did misunderstand - but it was a long post and they're not always the clearest things to read or write.

For "RAID stuff" substitute "RAID and backup stuff".

RAID is bloody useful but it is not a backup solution.

PS Somehow it has more of an "Oh f*ck, did I really do that" feeling than "Kodak moments"

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If the onboard IDE is a real drive, then I'd install the O/S there. If the onboard IDE device is a flash thingie, then I'd likely just put the /boot partition there, and everything else onto the RAID array. In fact, the latter is what I often recommend.

Cheers

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Meanwhile, I've got a couple of useless microdrives hanging around.)

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Use an IDE expansion PCI card (I'm thinking most often such cards are sold as 'raid controllers', but I haven't investigated this at all, so I may be going in the wrong direction) to allow more drives to be connected to the motherboard.

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Meanwhile, I've got a couple of useless microdrives hanging around.)

Open them up and frame them... I've never seen the inside of one, but I've always considered them an amazing technical accomplishment.

Presenting.. a GeoCaching "Travel Bug" in my honour: the actual item that was inside my camera at the 2003 Empeg Owners' Meet:



I tore the cover off, and later left it as loot in a geocache. Another local cacher retrieved it, and converted it into a "travel bug" named "Mlord's Micro Drive" (TBAF86).

Cheers

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What if I install Linux on an old 1GB microdrive through those CF/IDE adaptors like in the CF empeg thread!
(Just kidding- I'd expect performance would suffer. Meanwhile, I've got a couple of useless microdrives hanging around.)

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Still, nifty little things. Would you sell me one, and if so, for how much? (I miss my old ones).

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I'm curious what others think of this card or other similar cards. Should I just throw it in the garbage?

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Actually, you may or may not know that many cheap RAID cards are just simple multi-channel controllers - as this tongue-in-cheek FAQ says...

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many cheap RAID cards are just simple multi-channel controllers

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along with these to put my drives in - http://www.newegg.com/Product/Product.aspx?Item=N82E16817716034

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I wouldn't use their RAID capability - but if you have one then I'd use it as a multi-drive controller card.

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I can really see the disadvantage of not having any tools to monitor the array. I think that the drive would begin to recover, but when I re-booted it started over. I couldn't see a way of checking, even from the command line in freenas, what stage the rebuild was at. The only place tht told me that was the RAID's BIOS.

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...nifty little things...

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2 Pack of Hitachi 4GB Microdrive for $24.99 Shipped

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I found this set of instructions that I'm using as a loose guide for this:

http://www.debian-administration.org/articles/512

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Which brings me to another question. Anyone know of any drive monitoring software that can detect drive failures and send an email or an alert of some sort.

This is an automatically generated mail message from mdadm
running on haze

A DegradedArray event had been detected on md device /dev/md0.

Faithfully yours, etc.

P.S. The /proc/mdstat file currently contains the following:

Personalities : [raid1] [raid6] [raid5] [raid4] 
md1 : active raid5 sdd1[0] sda1[2] sdc1[1]
      390716672 blocks level 5, 64k chunk, algorithm 2 [3/3] [UUU]
      
md0 : active raid1 sdc2[1]
      3783232 blocks [2/1] [_U]
      
unused devices: <none>

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The article had three drives in the RAID1 array. Since RAID1 is mirroring, I've never seen 3 drives in a mirrored array. So I was wondering if one drive is actually mirrored to the other 2 in the array.

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So it sounds like this...someone correct me if I am wrong:

- All writes to the boot partition are mirrored to two other drives.
- If any one of the three drives fails, the fourth will automatically join the array so that the first partition is still mirrored to two others.
- If the first drive fails, then the system would boot off drive two which would then be mirrored to drive three and four.

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Yup, that's the idea. Many modern BIOSs will automatically do that last step (boot from first available drive) in particular.

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Disconnecting the power to the drive isn't the same thing at all, it is no different to disconnecting the SATA cable, which I have tested.

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Disconnecting the power to the drive isn't the same thing at all

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but how else are you going to test that without hacking a BIOS to control how a drive initializes at boot?

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but how else are you going to test that without hacking a BIOS to control how a drive initializes at boot?

I don't know, that was the whole point of asking if it was possible and if so how !

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I'd say a rubber mallet would work...

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I don't know, that was the whole point of asking if it was possible and if so how !