Does RAID 6+0 (60) increase performance with more drives?

Gabriel-M
Gabriel-M used Ask the Experts™
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Hi Experts,

I would like to know if I were to add more drives to a RAID 6+0 array if the performance would increase as well as capacity? Or would the performance remain the same?

I see that RAID 6+0 has 4 disks per set, and 2 sets, making 8.

How would the controller set it up if I had a 24 disk array? 6 sets of 4 per set? Or 2 sets of 12 per set?

Thank you very much for any help!
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RojoshoRTCC-III Level-2 Support
Commented:
Hello Gabriel-M,

The biggest advantage to RAID-60 is that you can have more than one disk go back in a set and still be able to recover your data; so from a data retention perspective, this is VERY GOOD.  BUT, having said that, a RAID-60 solution is going to take a performance hit due to the additional over head to calculate and write the extra parity sectors.

So, in answer to your questions...
Question #1:
Capacity will increase, but performance will drop a bit.

Question #2:
Performance will not remain the same and will dip a little, but your data is very secure.

I found this on the Wikipedia site which is VERY good in explaining the various RAIDs and the Pro's and Con's of each.
    http://en.wikipedia.org/wiki/Nested_RAID_levels#RAID_60_.28RAID_6.2B0.29

I hope this helped,

Cheers,

Rojosho

DavidPresident
Top Expert 2010

Commented:
"Performance" will increase the most on sequential reads.  If doing sequential writes, then it will usually increase.  If performing random I/O, then, in general, you will be better off creating additional arrays.  Remember that optimizing for IOPs and throughput are nearly mutually exclusive.   Your mileage may vary, as I/O characteristics vary considerably depending on the firmware and architecture of the controller, as well as the disk drives.  

For example, SAS drives have separate read and write channels, so write and read operations do not compete against each other for bandwidth.  The same can not be said for SCSI, and most SATA implementations.

Personally, I can't think of any real-world situation where 2x12 drives will be a good thing other than video streaming or data acquisition, and even then, it depends on the number of streams and disk technology.
Gary CaseRetired
Most Valuable Expert 2013
Top Expert 2009

Commented:
"... if I were to add more drives to a RAID 6+0 array if the performance would increase ..."  ==>   Yes.    Since you're adding more drives to the stripe, you'll get higher sustained transfer speeds.    However, this won't help with IOPs (as noted above), since the access characteristics won't change (you still need to seek to the data).    Bottom line:  Transfers will be quicker, but the impact on IOPs will be small (You'll see a slight gain).

"... How would the controller set it up if I had a 24 disk array? 6 sets of 4 per set? Or 2 sets of 12 per set?  "   ==>  The controller doesn't decide that -- YOU do.    As noted above, if your goal is to maximize IOPs, you're better off with multiple arrays;  if you want to maximize data transfer speeds, then a large number of drives will be best (i.e. 2 x 12 would have a very faster transfer rate).
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Author

Commented:
Thank you for the fast replies. Before I close this I want to make sure I understand this perfectly.

IOPs in this instance isn't as important as transfer speed (and of course security of the data) to me.

2 x 12 would be "faster" than 6 x 4 in theory?

Let me explain a little more.

             |-------------raid-0------------|
(raid-6)[12 disks]               (raid-6)[12 disks]

                                or

            |--------------------|--------------------|-------raid-0------|--------------------|--------------------|
(raid-6)[4 disks]  (raid-6)[4 disks]  (raid-6)[4 disks]  (raid-6)[4 disks]  (raid-6)[4 disks]  (raid-6)[4 disks]

I am assuming that 6 arrays of 4 disks each is better for data transfer speed?

Thank you for the help! I really appreciate it.

Author

Commented:
Also, which one my my examples is able to have a larger usable drive size?
DavidPresident
Top Expert 2010
Commented:
Fine, so you do not care about IOPs, just throughput, so that means mostly sequential access.  OK, it is your data, and I will give you benefit of doubt.
Exactly what controller & disk, and how will the disks be allocated to the 24 drive channels.  Reason I ask ... potential bus saturation.  Also, what is mix of Reads vs writes..  Bus saturation again.


Retired
Most Valuable Expert 2013
Top Expert 2009
Commented:
A RAID-6 witih 4 disks only has 2 disks of usable space, so you're using 1/2 of the disk space for fault tolerance.     A RAID-6 with 12 disks has 10 disks of usable space, so only 1/6th of the space is used for fault tolerance.    So 2 x 12 will provide 20 disks of usable space;  whereas 6 x 4 will provide 12 disks of usable space.

Author

Commented:
Alright, thank you (great answer garycase)! (dlethe: That would use another question thread to answer, and I will keep bus saturation in mind ;-) ). I think that just about answers it for me. I really appreciate all input. I'll close this question now.

Author

Commented:
Thanks everyone!
Gary CaseRetired
Most Valuable Expert 2013
Top Expert 2009

Commented:
Bus saturation (as mentioned above) can indeed be an issue -- but I'm assuming that if you have a controller that supports 24 drives it's on at least a PCIe x4 bus, so that shouldn't be an issue.    The AVSForum has an example of a 24-drive RAID-6 with an Areca controller that achieves a consistent 800MB/s with burst speeds over 1GB.    You should get fairly close to this with a 2 x 12 array.

Here's the HDTach display from the AVS thread:


hdtachareca256mbvc3.jpg

Author

Commented:
That's incredible. And yes, it will be on a PCIe card for sure, and at least 4x (if not 8 or 16). I haven't chosen the hardware yet. Still in the planning stages. Hence this question. Thank you SO MUCH everyone!!! <3
RojoshoRTCC-III Level-2 Support

Commented:
Gabriel-M,

You are welcome and thank you.

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