RAID10 disk size & quantity question

[jdcranke07]

Would it be better to have a larger capacity per HDD or would it be better to have a lesser capacity w/ an increased number of HDDs, in terms of redundancy?

I.e. Would having 6x8TB HDDs have any advantages over 24x2TB HDDs other than in chassis' w/ limited space?

In both cases RAID10 would be used & from what I can see speed increases would be much higher w/ increasing the number of HDDs. The only pro I see for the high capacity HDDs would be if I had limited space, right?

 

[USAFRet]

Impossible to suggest unless we know what use this is for, and why you're considering a RAID (whatever)

 

[jdcranke07]

Impossible to suggest unless we know what use this is for, and why you're considering a RAID (whatever)

NAS for media & backups. Mostly going to be reading off of the drives, not as much writing will be involved.
Currently using RAID5 for the parity on four 4TB drives since my current chassis can't handle that many drives. However, I am willing to get a chassis that can handle more drives if it will benefit over having higher capacity drives.

 

[USAFRet]

Impossible to suggest unless we know what use this is for, and why you're considering a RAID (whatever)

NAS for media & backups. Mostly going to be reading off of the drives, not as much writing will be involved.
Currently using RAID5 for the parity on four 4TB drives since my current chassis can't handle that many drives. However, I am willing to get a chassis that can handle more drives if it will benefit over having higher capacity drives.

Well...the more drives there are in a system increases the possibility of one or more failing.
24 drives is more likely to see a drive fail than 6 drives.

 

[therealduckofdeath]

Price vs performance is probably the biggest differentiator. Overall, I can imagine that the 6 disk RAID would be safer in the long run. Your examples are (to an extent) a 3 disk RAID0 vs a 12 disk RAID0. One real life thing that would add to the cost is that you'll need a RAID controller and enclosure large enough for 24 disks, which isn't particularly cheap. You will also run into four times as many disk failures per time frame, which is another expense. The utility bill will obviously also go up. Mechanical disks are relatively slow so the performance gain in your particular comparison would probably be quite substantial. Another downside with a 24 disk RAID10 is that the increased risk of data corruption, like write holes will obviously increase with each "chain" you'll add to a RAID10, so it's definitely not all benefits adding a lot of disks for redundancy. (A write hole will eventually destroy all data without the computer or controller realising it as it's writing over data thinking it's writing in empty sectors, they can occur simply by an overloaded controller, crashes, controller memory errors, cable issues, power spikes, random disk issues and whatnot)
Anyways, I would personally consider that a 24 disk RAID 10's a rather excessive number for a RAID. It's expensive for what you get and too many things can go wrong, probably making it less robust than a theoretical single 24TB disk.

(edit for too many numbers in the first line )

 

[USAFRet]

And no matter which configuration you eventually go for...that RAID array still needs its own backup.

My NAS box is a 4x4TB RAID 5. Backed up weekly to an 8TB USB connected drive.

 

[jdcranke07]

Price vs performance is probably the biggest differentiator. Overall, I can imagine that the 6 disk RAID would be safer in the long run. Your examples are (to an extent) a 3 disk RAID0 vs a 12 disk RAID0. One real life thing that would add to the cost is that you'll need a RAID controller and enclosure large enough for 24 disks, which isn't particularly cheap. You will also run into four times as many disk failures per time frame, which is another expense. The utility bill will obviously also go up. Mechanical disks are relatively slow so the performance gain in your particular comparison would probably be quite substantial. Another downside with a 24 disk RAID10 is that the increased risk of data corruption, like write holes will obviously increase with each "chain" you'll add to a RAID10, so it's definitely not all benefits adding a lot of disks for redundancy. (A write hole will eventually destroy all data without the computer or controller realising it as it's writing over data thinking it's writing in empty sectors, they can occur simply by an overloaded controller, crashes, controller memory errors, cable issues, power spikes, random disk issues and whatnot)
Anyways, I would personally consider that a 24 disk RAID 10's a rather excessive number for a RAID. It's expensive for what you get and too many things can go wrong, probably making it less robust than a theoretical single 24TB disk.

(edit for too many numbers in the first line )

So, essentially you're saying that it isn't really worth going the higher quantity vs higher capacity based on possible risk. Even w/ the 24 drives being cheaper than the 6, in the example I gave. I already have a HW RAID controller that can handle the number of drives already, so that's not really an issue, but I would have to get the drives and/or drives+enclosure depending to the route I take.

Now I ask because I've seen some ppl use more drives w/ lower capacities vs the fewer larger capacity drives for their setups & I was curious about why.

 

[therealduckofdeath]

I guess it depends on how much you would need the added performance. 24 disks in one array with a potential one disk limit on failure protection is a bit risky. For instance if it's not critical data that you can afford to lose and you have a real benefit with high performance it's obviously a valid option. But, you would need a UPS, I'd say. One unexpected power failure with that many active disks is almost guaranteed a broken array. I've seen companies who's kept running a large disk array for years with write holes without realising it, because most data doesn't crash anything when it's corrupted, so if you don't know you don't know.

 

[jdcranke07]

I guess it depends on how much you would need the added performance. 24 disks in one array with a potential one disk limit on failure protection is a bit risky. For instance if it's not critical data that you can afford to lose and you have a real benefit with high performance it's obviously a valid option. But, you would need a UPS, I'd say. One unexpected power failure with that many active disks is almost guaranteed a broken array. I've seen companies who's kept running a large disk array for years with write holes without realising it, because most data doesn't crash anything when it's corrupted, so if you don't know you don't know.

Thanks for the assist, guys.

 

[asoroka]

Also consider where the performance limit will come from.

On a NAS it will be the network card. So a 1Gb LAN will max out at 100MB/Sec sustained data rate.
Once you have 2 spindles, you are already over that performance bottleneck.

Unless you are talking about DAS, more than 2 spindles will not increase performance on a NAS.