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Old 07-15-2012, 07:11 PM   #1
BuckNekkid
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Cool RAID or not?


Hi,

I know a little about RAID and not the bug-killer kind. But,
I'm wondering how this would work out, say with 9 - 2 Terrabyte hard drives chained together? Now, wouldn't that give me an 18 terra-byte capacity?

Is there a motherboard with quad processors, and a large number of Ram slots to max out and has RAID on the board. It wouldn't have to have an on-board audio or graphics circuits. If there is I'll buy a good audio and video cards for that, LOL!

None of this would be set-up for gaming, just my ham radio digital modes pictures, mp3's and science experiments on radio propogation & weather, combined.

Thanks for looking,
Regards,

"Buck/KA5LQJ
 
Old 07-15-2012, 07:36 PM   #2
TobiSGD
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You would only get 18TB capacity if you setup the RAID in RAID 0 mode, which is meant to give you the maximum speed. The problem would be that you will loose all your data if only one disk fails.
The real questions are:
1. Why do you need 18TB storage space? Definitely not for pictures and mp3s, I don't know anything about the ham radio stuff, but I doubt that you will produce 18TB of data in a reasonable timespan.
2. Why do you want to use RAID? RAID is meant to minimize downtime in case of disk failure in critical systems.

To your other questions:
What do you mean with "quad processors"? If you mean a quad core processor, any recent board should be able to handle them. If you mean 4 CPUs on one board than prepare to give away a lot of many alone for the board, not to mention 4 server CPUs.
Any modern board has onboard audio, many have onboard video. You will not need a discrete video card if you are not into gaming.
Regarding the RAM, how much RAM do you plan to have and for what purpose? I have 16GB RAM in my main system (could handle 32GB) and that is more than enough for any purpose, even if I have parts of the file-system in RAM and run a couple of virtual machines simultaneously.

This whole thing sounds not very reasonable to me. I would recommend to go for a current mid-price system, with may be a 120GB SSD for the OS and a 2TB drive for the data. If your data-disk fills up just get another one. Don't forget to get one or two large external disks for your backups.
 
Old 07-15-2012, 07:45 PM   #3
jschiwal
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Raid 0 supplies no redundancy. If a single drive fails, the file system will be corrupt. With 9 drives it's 9 times as likely. you could use RAID 10 (raid 0 and raid 1). This would give you 2 * 4 TB using 8 drives. RAID 5 uses triplets of drives. 1/3 of the storage is used for parity. This allows 6 TB storage using 9 2TB drives.

Also look at LVM which can be used with raid.
 
Old 07-15-2012, 07:59 PM   #4
TobiSGD
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Quote:
Originally Posted by jschiwal View Post
RAID 5 uses triplets of drives. 1/3 of the storage is used for parity. This allows 6 TB storage using 9 2TB drives.
Should be 12GB, shouldn't it?
Keep in mind that you also will need a motherboard that can handle that amount of disks (+ a DVD drive or something like that?), most modern boards have 6 or 8 SATA ports.
 
Old 07-15-2012, 10:19 PM   #5
suicidaleggroll
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Quote:
Originally Posted by jschiwal View Post
RAID 5 uses triplets of drives. 1/3 of the storage is used for parity. This allows 6 TB storage using 9 2TB drives.
?

Where did you get that? That's not RAID 5, I don't know what that is. RAID 5 uses one drive for parity. Regardless of the number of drives in the array, only one is used for parity. So if you have a 4 drive array, you get the capacity of 3 of them. If you have a 9 drive array, you get the capacity of 8 of them. RAID 6 is similar, but uses two drives for parity. With 4 drives you get the capacity of 2, with 9 drives you get the capacity of 7.


With 9 drives I would lean toward RAID 6, provided you have a hardware RAID card capable of that kind of load. I wouldn't leave that much parity calculation to a software or "hybrid" RAID included on most motherboards, the overhead would just be too high IMO. Not to mention that I've never even seen a motherboard with that many SATA connections onboard. I also wouldn't trust an array that large to RAID 5, not unless you have a spare drive in the room and ready to go in the event of a failure (or you're willing to shut down the system as soon as a drive fails, and keep it down until you have a replacement drive ready to swap in).

IMO you're just losing too much space with RAID 1 or 10 with that number of drives with no real benefit (in addition to the odd number of drives causing issues in a typical mirror like that), and RAID 0 is just WAY too risky with that many drives. RAID 5 is still too risky IMO unless you have a spare drive ready to go, so in my mind that just leaves RAID 6.


FWIW - I have actively maintained 24/7 RAID systems for the last 7 years. I built and currently maintain three RAID 1, two RAID 10, six RAID 5, and four RAID 6 systems on various machines. I'm pretty familiar with the advantages and drawbacks of each setup, so ask away.

Last edited by suicidaleggroll; 07-15-2012 at 10:30 PM.
 
Old 07-16-2012, 10:03 AM   #6
BuckNekkid
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Red face Raid ?

Hi Guys,

I missunderstood what RAID was, I thought it meant you
could take up to 9 hard drives and add their capacities together
making it a "multiple drive" with a total space of 18 terabytes.
As it ran, it would put data like in 'series' and lessen the chance
of a disc failure.

Regards,
"Buck"/KA5LQJ
 
Old 07-16-2012, 02:28 PM   #7
NyteOwl
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If you mean just create one large 18TB drive then yes you can do this. It's called drive concatenation and is sometimes referred to as a spanned or "BIG" drive. You can do this in Linux using LVM.

RAID doesn't reduce the chance of disk failure, it reduces the chance of losing data because of a disk failure, and improves the ability to recover from same. Despite it's common usage RAID 0 is actually an oxymoron.

And of course, despite using RAID one should always have backups.
 
Old 07-16-2012, 03:23 PM   #8
jefro
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Even my wife would take a few months to fill up 18Tb. I doubt you would need anywhere near that in the short term.

Think about a backup solution instead.
 
Old 07-16-2012, 03:25 PM   #9
lithos
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Quote:
Originally Posted by TobiSGD View Post
Quote:
Originally Posted by jschiwal View Post
RAID 5 uses triplets of drives. 1/3 of the storage is used for parity. This allows 6 TB storage using 9 2TB drives.
Should be 12GB, shouldn't it?
Keep in mind that you also will need a motherboard that can handle that amount of disks (+ a DVD drive or something like that?), most modern boards have 6 or 8 SATA ports.
In fact that would be 16TB (sum all drive no. -1 <-- raid calculator).

But,
I don't know there is a server board with onboard RAID for let's say 8 drives, just RAID controller cards (even with 12 or more ports)
and a quick sum of prices would be:
- Adaptec RAID 31205 controller = $ 300
- 9x 2TB drive Enterprise class = 9x $ 300 = $ 2700

Total sum: $ 3000
only for storage
+ another $1500 a server with some 16GB RAM (just a price in my head from last search a month ago)


Here a quick RAID types explanation.

I hope it will be explained what on earth is the purpose of THAT much storage space needed.

Regards

Last edited by lithos; 07-16-2012 at 03:51 PM.
 
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Old 07-16-2012, 04:05 PM   #10
TobiSGD
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Quote:
Originally Posted by lithos View Post
In fact that would be 16TB (sum all drive no. -1 <-- raid calculator).
I think I fell into the same triplet hole as jschiwal, just because I sometimes use RAID 5 with three drives and then it comes up to 2/3 storage capacity. Thanks for the correction.
 
Old 07-16-2012, 05:14 PM   #11
suicidaleggroll
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Quote:
Originally Posted by BuckNekkid View Post
Hi Guys,

I missunderstood what RAID was, I thought it meant you
could take up to 9 hard drives and add their capacities together
making it a "multiple drive" with a total space of 18 terabytes.
As it ran, it would put data like in 'series' and lessen the chance
of a disc failure.

Regards,
"Buck"/KA5LQJ
That is what RAID does, but you can't use the capacity of all of the drives if you want some kind of redundancy. Think about it. If you had all 18TB full of data, and a drive failed, how could the system know what was on the drive that failed? There is no extra room available to store any kind of backup or parity information of the data that's on your array. What you described is RAID 0, where the data you write to the array is striped across all drives in the array. This provides no redundancy though, in fact it makes things worse than with a single drive, because you're now 9 times more likely for a single drive to fail (since you have 9 drives), which means you're 9 times more likely to lose data.

If you want any kind of protection against data loss in the event of a disk failure, then you need to give up some of that 18TB for redundancy. That's what the different RAID levels are for. RAID 5 gives up one drive (so you would have a 16TB array), so that you can lose any single drive in the array without losing data. RAID 6 gives up two drives (so you would have a 14TB array), so that you can lose any two drives in the array without losing data. RAID 10 gives up half the drives (so you would have an 8TB array, plus one extra drive), and would essentially consist of two RAID 0 arrays of 4 drives each, mirrored with each other. So if you lose any drive, that half of the mirror will the lost, but the other half will still be good.

You can never prevent disc failure, but RAID helps to prevent data loss in the event of disc failure. In my experience, with 9 drives you'll likely lose one drive every 3-4 years (that will accelerate after a decade or so) if you have them cooled well, 1-2 years if they're not cooled well. If you're not prepared to lose all of the data on that drive when it fails, then you need to have some kind of backup or redundancy solution such as RAID.
 
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Old 07-16-2012, 05:29 PM   #12
TobiSGD
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Quote:
Originally Posted by suicidaleggroll View Post
If you're not prepared to lose all of the data on that drive when it fails, then you need to have some kind of backup or redundancy solution such as RAID.
Just to emphasize what NyteOwl and jefro already said, so that this isn't misunderstood. A RAID is in no way a replacement for a backup solution. Regardless if you have RAID 1, 5, 6, 10 or whichever RAID level, if your data is important to you you always need a separate backup solution. No offense to suicidaleggroll, I know that you know that, but this sound s a bit ambiguous.
 
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Old 07-16-2012, 05:47 PM   #13
suicidaleggroll
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Quote:
Originally Posted by TobiSGD View Post
Just to emphasize what NyteOwl and jefro already said, so that this isn't misunderstood. A RAID is in no way a replacement for a backup solution. Regardless if you have RAID 1, 5, 6, 10 or whichever RAID level, if your data is important to you you always need a separate backup solution. No offense to suicidaleggroll, I know that you know that, but this sound s a bit ambiguous.
Yes, that is very true. RAID will protect against drive failure, but something like a power surge or a power supply failure could easily wipe out the entire machine and every hard drive attached to it, RAID will do nothing in that case.

I had a system a few years ago that was running fine and then just died one day. After some debugging I discovered the power supply had croaked, so I swapped in a new PS and tried again, still nothing. It was an older system anyway, so I just scrapped it and built a new one. Once the new one was up and running, I attached one of the hard drives from the previous machine so I could pull some data off of it. I tried turning on the computer with the old drive attached, but it hung at the BIOS splash screen, seemed completely frozen. I peeked my head around the corner of the case and saw that the hard drive I had just plugged in was on fire...literally. 3-4" flames licking off of the drive's circuit board. Turns out when the power supply in the last machine failed, it sent a huge surge through the entire machine and blew up the power circuitry in the hard drive that was attached. So when I attached that drive to a new, working machine, it short circuited and lit on fire.

Long story short, make backups regardless of how "bulletproof" the system might seem.

Last edited by suicidaleggroll; 07-16-2012 at 05:49 PM.
 
Old 07-16-2012, 05:57 PM   #14
273
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I'd like to add my amateur dealings with RAID here also:
When I bought my PC a few years ago I specified a software RAID5 of 3 drives for my home partition, this meant I lost the capacity of one drive but if one died I'd still have my data.
Over the years (about 5) I have had some cases where one drive has developed errors, so the RAID rebuilt. I've managed to wipe my RAID once, and thought I did twice. When I updated my PC recently I almost lost the RAID too due to not being careful mounting it.
I also have an external 1TB drive. I used to use it through ESATA and it has been giving SMART errors (hardware faults that say it's dying) for a year or two now. Yet I'm still running VMs from it.

My point is that I am now planing on buying an internal 1TB disk and an external one too and keeping my data on both. I did this between the RAID and ESATA drive anyhow, but I gained nothing by the RAID setup.
Backup is key. Unless, of course, you run systems which must continue to be resilient under disk failure but, then, you'll probably know which RAID level you want because you will ahve to have studied the possibilities.
For home use -- duplicate your data, get a backup strategy, expect disks to die.

Last edited by 273; 07-16-2012 at 05:58 PM.
 
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Old 07-24-2012, 04:17 PM   #15
BuckNekkid
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Talking NOT "Raid", LOL!

Howdy Guys, C'est Moi!

I'm begining to see what I was thinking of did not fall within the properly formed ideas. What I was shoot for was the maximum amount of disc space for storage. I understood that RAID fell within this catagory. I misunderstood that Raid supported 9 hard drives daiy-changed together, so a present day 2 tb drive would equal out to 18TB. Now this mistaken idea does not support 9 drives and it would be hard to recover data from a RAID drive.

Now, I know about making backups which is the right way to go and I was trying to do a get-@round for it. So, I'll just get a 2Tb drive and fill'er up, I'll have to learn how Linux does
it's backing-up.

Respectfully submitted,
Regards,

Buck/KA5LQJ

Last edited by BuckNekkid; 07-24-2012 at 04:25 PM. Reason: I fell asleep.
 
  


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