I don't get RAID 5 ...

theurbanclown

theurbanclown

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Can someone please explain in simple terms.

Bought a Qnap TS420 about a week ago. Setup RAID 5 which took forever.

I have 2 x 3tb WD Red Drives and 1 x 1.5tb Samsung Drive. After setting up the RAID 5 config I only have just under 3tb of usuable space. I was under the impression that I'd of had around 4tb of usable space (1 x 3tb and 1 x 1.5tb) with the remaining 3tb ready to step in, in the result of a drive failure. This is not the case, and don't understand why I essentially have a 3tb sitting do nothing.

Can somebody explain in simple terms if it is right, why so?

And if it isn't, is it possible I have I done something wrong in the setup? Is there a different RAID option that would allow me to do create the scenario I want?

I'd be just as well off with 3 x 1.5tb drives as it stands.
 
I suspect it's because you are using a 1.5 tb drive in there. You can only have a raid of twice the size of the smallest drive in a set up like that.
 
If you had a 3rd 3Tb drive instead of the 1.5Tb, you should have 6Tb usable, but your 1.5Tb dictates the maximum size of the R5 partition. With RAID 5, any single one of your discs can die, and the array can be rebuilt safely, because of the way the failure protection works. If you think about it, what you are seeing makes sense. To enable any 1 disc to fail, and for the remaining 2 to rebuild themselves, the data protected cannot be larger than the size of the smallest disc. As a rule of thumb with 3 drives, your storage capacity will 2 x the size of the smallest drive, hence what you are seeing. RAID5 is very good and can be quite efficient. I have a 4 drive RAID5 setup on my desktop PC that has been running for years now. I have 4 x 400Gb drives, and with 4 drives, you still lose 1 drive to parity, so I have 1.2Tb of resilient storage. I've had 1 drive fail in the array, and getting back up and running was a simple as replacing the failed unit and the array rebuilt. Some NAS's allow you to have a mixed R5 and simple partition. If yours allows that, you could have 3Tb of RAID 5 protected storage and 3Tb of plain (vulnerable) space. I'll upgrade mine one day as it's getting full, but I back up from there to a NAS mirror, and will need to upgrade that as well. Belt and braces I guess, but I haven't lost data for a long time to disk failure.
 
Yup, as others have said as you have a 1.5tb drive in there you'll be limiting all of the other drives to 1.5tb too.

If you had 3x 3tb I raid 5 you'd have 6tb (minus overheads), 4x 3tb you'd have 9tb etc. Essentiall with raid 5 add all of the drive sizes together then minus one drive size, but you need the drives all of the same size.
 
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Unless you've got a drobo in which case all previous raid calculations might as well be binned :(
 
mac124 said:
I suspect it's because you are using a 1.5 tb drive in there. You can only have a raid of twice the size of the smallest drive in a set up like that.
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neil_g said:
Yup, as others have said as you have a 1.5tb drive in there you'll be limiting all of the other drives to 1.5tb too.

If you had 3x 3tb I raid 5 you'd have 6tb (minus overheads), 4x 3tb you'd have 9tb etc. Essentiall with raid 5 add all of the drive sizes together then minus one drive size, but you need the drives all of the same size.
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DuncanDisorderly said:
Yup...
See http://superuser.com/questions/3801...d-5-with-a-bunch-of-drives-of-different-sizes
The smallest drive is the limiting factor.
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Simes123 said:
If you had a 3rd 3Tb drive instead of the 1.5Tb, you should have 6Tb usable, but your 1.5Tb dictates the maximum size of the R5 partition. With RAID 5, any single one of your discs can die, and the array can be rebuilt safely, because of the way the failure protection works.
Click to expand...

Cheers guys. I just assumed that because I had the 2 x 3tb and a 1.5tb, that if either the 3tb or 1.5tb failed then the other 3tb drive would step in to cover the loss of drive space as it's big enough but I kind of get it now.

I have another 1.5tb drive that I might add to the array to get 4tb - although then I'd be no worse off using RAID 1. This is getting expensive.
 
theurbanclown said:
Please explain.
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Drobo uses a system called "BeyondRAID" which will analyse the disks for you and give you the most available space whilst also being protected. In this scenario it will give you 4.08Tb with your current disks, although the flexibility also means that you technically don't know how the protection is working, as in Mirror, Parity, etc...

Drobo may be good and I've certainly heard some good things about it, but hell will have to freeze over before I consider giving up my Synology!

And if you think RAID can be confusing, NEVER look at Fluid Data Storage Technology, effectively where data 'flows' between various RAID levels in real-time for optimal data access.

Anyways, hope what I've written kind of made sense!
 
Neilc28 said:
Drobo uses a system called "BeyondRAID" which will analyse the disks for you and give you the most available space whilst also being protected. In this scenario it will give you 4.08Tb with your current disks, although the flexibility also means that you technically don't know how the protection is working, as in Mirror, Parity, etc...

Drobo may be good and I've certainly heard some good things about it, but hell will have to freeze over before I consider giving up my Synology!

And if you think RAID can be confusing, NEVER look at Fluid Data Storage Technology, effectively where data 'flows' between various RAID levels in real-time for optimal data access.

Anyways, hope what I've written kind of made sense!
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Yes, remember seeing this actually - thanks for explaining it a bit further though. I think I may have actually used the Drobo calculator which I think furthered my belief that I'd get around 4tb usable space.

Think I'll give fluid data a miss. Head hurts.

neil_g said:
Synology > drobo.

I've heard horror stories with drobo and data loss, proprietary file systems and poor support.
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Yeah, I'm more than happy with my Qnap too. And got it for a bit of a bargain (£245 new)
 
theurbanclown said:
I have another 1.5tb drive that I might add to the array to get 4tb - although then I'd be no worse off using RAID 1. This is getting expensive.
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RAID 10 might be a good choice as you have different sized disks, alternatively just do two sets of two RAID 1 arrays unless you need to have one location for your data.

With the drives you've got two RAID 1 arrays would be my preference and just be careful how you manage your data.
 
I have a drobo, had it for 3 years, real time hot disk swap, done it too and it works by just pulling out the smallest disk and put in a newer bigger one.

I also have a Netgear NAS with 4x 3TB drives running it's own X-Raid which supposed to do the same thing but I don't plan to test it as I don't intend to increase the size of the NAS.

Both system are good, Drobo has been flawless, Netgear had a few hiccups early on but I've fixed it all now.
 
Procurve switch and Synology NAS, the winning combo in my opinion! I've had Netgear before, at both work and home, and from a home-user perspective it's ok, but if you want to make the most of potential network speed and 100% uptime then it's not the solution, I have unfortunately seen one too many locked-up Netgear switches with all of the port light indicators illuminated solid, power-cycle time!
 
Transferring all of my data across now. Speeds are terrible over wireless - about 1MB/s.

Qnap is connected to router via cat5e cable and PC is connected via wireless. I knew it would be a lot slower than wired, but not this slow!
 
neil_g said:
yup wireless will be awful for transfer.

even if its temporary while you transfer data wire them. but personally id say gigabit it all.
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Annoyingly I have a 20m Cat5e cable, but it's at my parents and won't be there anytime soon. Just bought a pair of Home Plugs (500 mbps) and will pick them up in a bit - I imagine that will improve things a great deal, even though it's not gigabit.
 
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