Sign in with
Sign up | Sign in
Your question
Solved

Setting up a raid 6 on the cheap?

Last response: in Storage
Share
March 14, 2014 6:49:38 PM

Hi all...

Wondering there's a way to set up an 8-drive raid 6 using cheap, consumer level drives? I've done it for servers but I'm hoping it can be done without enterprise-grade drives and $400 (on the cheap end) controller cards. Any mobos out there with enough connectors, or cheap cards that have a raid 6 mode, that anyone knows of?

Thanks^^

More about : setting raid cheap

a c 115 G Storage
March 14, 2014 7:08:59 PM

Unfortunately, Intel and AMD's chipset controllers only stretch to 6 drives. Any more, and you have to spread it across different controllers and do it in software. Plus, I don't think you can do RAID6 on those controllers.
m
0
l

Best solution

a b G Storage
March 14, 2014 8:26:49 PM

If you're asking "will desktop hard drives work with a SAS raid controller?" then the answer is a very definitive YES.

My home server runs with an adaptec 3805 128MB, along with a intel SAS expander, it is currently host to a 10 disc (all laptop hard drives) raid 5 array. I know this isn't raid 6 but raid 6 is available to the drives should I want to configure it.
Share
Related resources
March 15, 2014 1:31:51 PM

pauls3743 said:
If you're asking "will desktop hard drives work with a SAS raid controller?" then the answer is a very definitive YES.

My home server runs with an adaptec 3805 128MB, along with a intel SAS expander, it is currently host to a 10 disc (all laptop hard drives) raid 5 array. I know this isn't raid 6 but raid 6 is available to the drives should I want to configure it.


Well, I was actually hoping there might be a lower end controller that doesn't necessarily use SAS, but still, that's good to know. Thanks!
m
0
l
March 15, 2014 1:32:35 PM

Someone Somewhere said:
Unfortunately, Intel and AMD's chipset controllers only stretch to 6 drives. Any more, and you have to spread it across different controllers and do it in software. Plus, I don't think you can do RAID6 on those controllers.


Yeah, the ones I've looked at only go to raid 5...
m
0
l
a c 115 G Storage
March 15, 2014 5:57:20 PM

The other option is to do all the RAID in software. Somewhat slower and resource-intensive, but you can spread it across controllers and do it on any number of drives you want.
m
0
l
a b G Storage
March 17, 2014 4:31:44 PM

Someone Somewhere said:
The other option is to do all the RAID in software. Somewhat slower and resource-intensive, but you can spread it across controllers and do it on any number of drives you want.


Yes, you can do this, but would you really recommend someone use 8 modern(1TB+) consumer drives in RAID 6?

Even assuming nothing else goes wrong, you've got greater than a 1/4 chance of failing during the rebuild with a 6TB RAID 6 with 1TB drives as an example.

RAID 5 and 6 are obsolete for modern consumer drives IMO.
m
0
l
a b G Storage
March 17, 2014 4:52:19 PM

Please post your sources for this ridiculous statement.
m
0
l
a b G Storage
March 17, 2014 6:00:53 PM

smitbret said:
Please post your sources for this ridiculous statement.


The sources for what? The UBE rate for consumer drives? Or do you want me to explain how RAID and RAID rebuilds work?

Clarify please.
m
0
l
a b G Storage
March 17, 2014 6:43:33 PM

I've just never seen a software RAID 6 rebuild fail with enterprise or consumer grade HDDs. So, I was just wondering where you got your 25% failure rate for RAID 6 rebuilds.

For home and general consumer use, RAID 5 & 6 are the ideal solution.
m
0
l
a b G Storage
March 18, 2014 9:15:22 AM

smitbret said:
I've just never seen a software RAID 6 rebuild fail with enterprise or consumer grade HDDs. So, I was just wondering where you got your 25% failure rate for RAID 6 rebuilds.

For home and general consumer use, RAID 5 & 6 are the ideal solution.


Whether it's software or hardware RAID, the recalculation is done on the disks with the same limits.

Consumer drives have Unrecoverable bit error rates at 10^-14 bits which is 12TB.

That means if you've got 8 X 1TB consumer drives in RAID 6, the chance of encountering and unrecoverable bit error when recalculating parity is ~50%. Of course, since you've got 2 drive parity, assuming you know which drive encountered the error(this is a pretty big assumption) you can attempt a second rebuild, which will also have a ~50% base chance of failing. that's where I got the ~25% base chance of a failed rebuild.

The difference with NAS/Enterprise drives is they have a 10^-16, which brings the base rebuild failure probability below 1%.

You can always find anecdotal evidence where rebuilds have mostly been successful, but the probabilities don't lie. If you do 100 rebuilds in similar systems you will tend toward ~25% resulting in inconsistent parity data due to failed rebuilds and that's assuming nothing else goes wrong.
m
0
l
a c 115 G Storage
March 18, 2014 7:02:20 PM

The big question, of course, is how close those drives are to their specified error rates.

The other question is whether one wrong bit screws up the whole rebuild, or if it will continue and you just have one file that won't checksum correctly.
m
0
l
a b G Storage
March 18, 2014 8:31:03 PM

Someone Somewhere said:
The big question, of course, is how close those drives are to their specified error rates.

The other question is whether one wrong bit screws up the whole rebuild, or if it will continue and you just have one file that won't checksum correctly.


With consumer and no TLER, one drive usually falls out of the array and the rebuild stops. That's what you should expect to happen and not count on that it won't.

The best case scenario is not that the recalculation continues on its own without further corruption but that it stops and that the controller/software available can restart the rebuild or you have the know how to identify where it stopped and manually rebuild the array.

Either way, everything comes to a grinding halt while you do this(or restore from backup if it's faster).

Further, the UBER is defined primarily by the controller and built in error correction which is an architectural choice. If the rating was closer to 10^-15 they would advertise as much, but even then it would be unacceptably high.
m
0
l
!