Am I wrong? Swapping RAID disks between controllers

RazorWind

Supreme [H]ardness
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Here's my situation. My employer is buying a piece of aerial surveying equipment that apparently stores the data it collects on a RAID 5 array, which is connected to its host Windows PC via USB 3.

The boss guy from the vendor claims that the proper procedure for extracting the data from the instrument is to remove the five bare disks from the RAID enclosure, and plug them into another identical RAID enclosure, which will recognize them as a configured array. I'll admit my experience with RAID systems is limited, but in my 15 years in the IT world, I've never heard anyone actually endorse doing this as a standard operating procedure before.

This is the enclosure they're using. There's a manual available for download, which doesn't seem to say whether or not it's supposed to support this.
http://ain.mediasonic.ca/store/product_info.php?cPath=71&products_id=257

I've always heard from more experienced folk that messing with configured RAID arrays is a really bad idea. My limited experience agrees. I have some LSI controllers that support exporting the array configuration, so you can replace the controller, but I've never been able to get it to work right when I tried it.

My suggested fix is to make the entire RAID box removable, with the drives inside. Between flights, we'd simply swap out the entire box, like any other external hard drive. They dismiss this as too difficult, because it's "too late in the game to be making changes."

Am I wrong in thinking that this is a really half-assed solution?
 

Cool1Net6

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To my knowledge, what boss vendor said is possible; as long as all of the RAID hardware is IDENTICAL (down to the firmware) you should be able to just swap drives. However, I have only ever heard this in the even of a RAID card/enclosure failure. I have NEVER heard of pulling RAID drives as SOP in any way, and frankly am a little shocked that would be recommended at all for anything short of data recovery.

If your superiors care about the safety of their data at all, they would heed your advice and make the damn box removable.
 

TeeJayHoward

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If your superiors care about the safety of their data at all, they would heed your advice and make the damn box removable.
This. I ruined an array back in the day by taking the drives out, and putting them in identical hardware. I apparently forgot to note which drive was connected to which port on the controller, and that is all it took. It's not an issue with modern software raid systems, thankfully. I've pulled my Storage Spaces array out, swapped the disks around, and plugged it back in to a different computer (with completely different hardware). Windows recognized what disk was what, and none of my data was lost. I've done the same thing with ZFS. Everything worked great.

But hey, if the vendor is willing to accept all liability for the potential screw ups...
 

RazorWind

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If your superiors care about the safety of their data at all, they would heed your advice and make the damn box removable.

Thankfully, it sounds like all it it'll take to make the box removable is a few thumb screws.
I will likely be the primary operator and repair tech for this thing, so I think I can totally get away with that modification, but I feel like I shouldn't have to do that to something brand new that costs as much as it does.

What I'm really worried about at this point is all the other things they may have half assed that I don't know about yet, and can't fix so easily.
 

RazorWind

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And you can't extract the data via USB 3?

Sounds very poorly designed.

The USB3 interface is part of the RAID box, which the vendor didn't intend to be removable. I agree, that's a stupid design. Our other airborne instruments have hot swap bays for single, non-raid disks.

This wouldn't be a problem, except the instrument in question gets installed in an aircraft, and gets its power from the aircraft's electrical system. We could conceivably copy the data from the flight disks to something else directly from the instrument, but that would require that we sit there on the ramp with the engine running while it was copying, which is an expensive proposition when you have to copy terabytes of data, and engine runtime costs hundreds of dollars an hour.

Also, the machine that the data get copied to weighs 300 pounds, and is the size of a small refrigerator. Not practical to set that up on the ramp, either.
 

staticlag

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If it was me, I would see how much data could be generated and see if I could set it up as a RAID 1 or RAID 10.

If you have just 2, 4TB drives inside mirrored then you could just pull one to xfer the data without much risk.
 

RazorWind

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If it was me, I would see how much data could be generated and see if I could set it up as a RAID 1 or RAID 10.

If you have just 2, 4TB drives inside mirrored then you could just pull one to xfer the data without much risk.

Does RAID 1 actually just make two copies of the disk, as if it were a standalone? I would have assumed that you'd still need the RAID controller to be able to read it. I guess it probably varies by implementation.

Also, I think the RAID may be there for performance, as well. The peak data rate from the instrument to the storage device is supposedly in excess of 200 MB/s. I'm skeptical that this RAID box can actually write that quickly with only four disks, but the vendor guy seems pretty confident.
 

Atari911

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I have done this using the Linux kernel and have had no problems. This seems like a fine solution if it is only being done once in a while but not as regular operating procedure. Especially if it is not hot swapable. Why is it not hot swapable!?!?!
 

RazorWind

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I have done this using the Linux kernel and have had no problems. This seems like a fine solution if it is only being done once in a while but not as regular operating procedure. Especially if it is not hot swapable. Why is it not hot swapable!?!?!

I assume the enclosure itself is hot swappable if it's a USB3 device.

The reason the drives themselves aren't hot swappable is that, for some reason, the vendor in question has never actually been asked to make the storage removable before. How they've managed that, I have no idea, as we're talking multiple terabytes of data that you somehow have to extract from the thing after each flight, but that seems to be how this happened.
 

Atari911

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Yea, that's what seems strange to me. You think that they would have made it more friendly to this type of procedure if this was in fact proper procedure.
 

GeorgeHR

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Also, I think the RAID may be there for performance, as well. The peak data rate from the instrument to the storage device is supposedly in excess of 200 MB/s. I'm skeptical that this RAID box can actually write that quickly with only four disks, but the vendor guy seems pretty confident.

SATA II hard drives are about 100MB/s. So 200MB/s is reasonable for RAID with 4 drives.

Using 200MB/sec 1TB takes 1.5 hours to transfer to another device. Much cheaper labor wise to physically move the disks rather than the drives.

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It is easy enough to test if you can move the drives from one box to another. Buy a second box. Copy some files to the drives in one box. Move the drives. Try to read the files.
 
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