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Readynas not recognizing true size of hard drive. 4TB X 4 = 10TB only available?
So I have 4TB drives X 4 of them which should be around 16TB, subtract one for parity and you get 12TB. If each 4TB drive is only 3721, and 1 drive is for parity, I should still have 11,163 T...
Welcome to the world of overhead and rounding :D (I'll avoid listing BS as well)
You can check NETGEAR's RAID calculator for a bit more information: http://rdconfigurator.netgear.com/raid/index.html
1) 4HDDs in XRAID mode = RAID5, so as you said, one HDD is for parity
2) A few GB of all HDDs are used for volume & swap
3) HDD manufacturers made up something called TB & TiB. Instead of counting by multiples of 1024, they count in multiples of 1000. So a 4TB HDD is not 4 (T) * 1024 (G) * 1024 (M) * 1024 (K) * 1024 Bytes but 4 (T), 000 (G), 000 (M), 000 (K), 000 Bytes. They call the first one 4TiB. Computers have never counted in multiples of 1000, but that's what you can do with money & good lawyers to win lawsuits.
4) When a volume is formatted, you need to count some overhead for the filesystem.
5) After counting all this, you should get something like 10.9TiB. But the GUI rounds (or I should say truncates) it to 10TB.
You can also notice that it's 10TB when it "should" be 10TiB. But really, TiB is just something made up by HDD manufacturers.
https://en.wikipedia.org/wiki/Binary_prefix#Consumer_confusion
So it does actually add up ;)
Thank you for the extremely detailed response.
I do know about the 1,000 vs 1024 hard drive thing, overhead ,etc.. However, I did realize that Netgear/Infrant Readynas would round 10.9TB DOWN to 10TB. I guess that is what threw me off if that is what is happening. I mapped a network drive to my computer and it showing up as 10.8TB so you must have hit the nail on the head with your answer.
I am looking at that calculator and I did not realize that you could mix and match so many odd sizes of raid. I did not realize you could do that without counter all hard drives as the smallest of the array.
For example, If you combine 2TB, 3TB and 4TB drtives, all drives would act like a 2TB drive.
They must shuffle around the parity data between multiple drives instead of having 1 isolated drive for parity.
Thanks for solving my problem.
Only X-RAID on our legacy Sparc devices (discontinued several years ago now) used a dedicated parity drive. All our newer products use distributed parity for all redundant RAID modes.
Using X-RAID2 we use multiple RAID layers. So say you had 4x4TB disks and replace 2 of them with 6TB disks (one at a time of course, wait until resync completes before replacing next disk). You would have a 4x4TB RAID-5 layer and a 2x2TB RAID-1 layer. So you'd get about 1.8TiB of vertical expansion. We can only expand volumes when redundant space can be added, so adding a single 6TB disk wouldn't result in any vertical expansion (you would need at least two 6TB disks in the system to get vertical expansion when adding 6TB disks).
If you were using X-RAID2 dual-redundancy (uses RAID-6) you would need four higher capacity disks to get vertical expansion.
RAIDiator-x86 4.2.x does have two expansion limitations
1. You cannot expand a volume by more than 8TiB over the life of the volume. So if it was say 1.8TB when you created it (e.g. when doing a factory reset) you couldn't expand it beyond 9.8TiB
2. You cannot expand past 16TiB. To get a volume capacity larger than 16TiB (this could happen e.g. using 4x6TB disks in RAID-5) you would need to do a factory default (wipes all data, settings, everything) with the disks in place.
ReadyNAS OS 6 doesn't have these expansion limitations.
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