Hardware Upgrade recomendations needed!

[CatMan]

Alright!
I have had my freenas server for a while now, truly enjoying it!
Build FreeNAS-9.1.1-RELEASE-x64 (a752d35)
MB: MSI 790fx-gd70
(Patriot sector 5) 8gb dd53 ram
AMD Phenom(tm) II X4 955 Processor (black edition)

Using ZFS:
3x WD green 2tb in a raidz
2x samsung f4 2tb in a raid 1


I would like to keep the box and sell/upgrade the drives.
I was looking and considering WD nas RED line.
8x 3tb WD red. on the ServeRAID M1015 controller. (Based on recommendations here I would like to get a ServeRAID M1015 (Crossflashed to IT mode)


I see a difference across raid calculators, for example this one on Synologys website:
http://www.synology.com/support/RAID_calculator.php?lang=us
No matter how many 3tb drives I add to a RAID6 pool, it always shows 6tb for protection.
Is this just a synology thing?

Advice is needed.
Thank you Greatly!!

 

[MtK]

look for the spec/definition of Raid6. it uses a minimum of three drives and always uses 2 for parity (regardless if the total amount if drives).
so u'll get P=2 and Total Size=(N-2)*(size of smallest disk)

 

[CatMan]

Hmm, Alright thank you!
So why is it that I see some people saying Raid 6 will protect your data, others saying its useless?
I know it's always best to have another offline backup as well.

 

[MtK]

well, leaving aside the performace aspects, it's simple math.
if you have 4 drive and 2 are parity, you have better redundancy than if you have 100 disks and 2 are parity, right?
also the more disks you have, the chances of a disk to fail increase, that's why vdevs are usrd with small groups of disks, creating one large pool.
(read the presentation in cyberjock's signature)

i think you are confusing that claim with raid5 that usrs 1 disk for parity. so if it fails your pool is still alive, but while the system resilvers the new disk, another disk might fail... and... bye bye pool :-(

 

[gpsguy]

look at getting some additional RAM if you replace your drives.


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