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How will unraid handle several raids ?


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Hello :)


i'm new to the forum and searched a while for a media storage & cheap solution with a bit of secure data storage -> voila unraid.


I'm reading since about 2 weeks many threads due to planning, cases, hdd types etc in order to exchange or upgrade my hp microserver. Because i have one xeon x5660 more than needed i built a new system, in the future virtuallized.


now the question: I see some people create for the cache drive or parity drive a 2 disk raid 1 because unraid counts that as 1 drive. How will unraid count several raid 1 or raid 5 for storage ? Each raidset as 1 drive ?


I hope i didn't miss the answer in this great forum!



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I agree with peter,


it is counter intuitive to place a fake raid system on top of a real raid system.


You just loose performance and drive space, waste electricity and gain no added protection.



with the new way the cache drive works in the latest betas... a large raid5/6 array for a cache drive sounds very tempting suddenly.

assuming unRAID sees the raid5..

you could use unRAID as a self contained, automated tiered storage system.

A tier1 high performance storage system on the raid5 with a tier2 storage sub-system on the unRAID array...

you would gain the the write speed to the Tier2 storage at the performance level of the tier1. all at the same time you can use the cache drive as the tier1 all while using the mover as intended and keeping your data secure.


to bad I don't have the cash on hand to test this..



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I have an Areca ARC-1200 - which is a 2 port PCIe x1 hardware RAID card, pretty well supported by unRAID (no temperature data, no SMART data, and it manages its spinup/spindown state, but otherwise works great).  As far as I know, it is the only true RAID card anyone has tried by unRAID.  Both WeeboTech and I both use this card.


I have three volumes on the card -

- 3T RAID0 - Parity Volume

- 1T RAID1 - Secure Data Volumne (since this is RAID1, it is really taking up 2T of space to provide 1T of mirrored space)

- 1T RAID0 - Cache Volume (not being used)


I plan to merge the parity and cache volumes to create a 4T RAID0 parity volume.  Having parity and cache on the same physical disks didn't work very well, hence I don't use the cache volume as my cache disk. 


The secure data volume is not part of unRAID, but is a separately mounted filesystem.  I use it for personal data (My Documents, etc.).  It is a bit faster that unRAID, especially for writing.  It is also more secure.  Each member of my family has a dedicated share on this volume for their personal files.


The RAID0 parity has several advantages:


1 - It provides faster writes, especially when writing to multiple unRAID disks at the same time

2 - It enables me to create a larger parity volume than a single disk.  So when 4T drives come out, I can configure my RAID0 parity volume to be 4T (eliminating the cache volume) and buy just ONE of the 4T drives to use as a data disk.  Those that have been around for a while know that it painful to have to buy TWO of the expensive next larger drives to get any benefit.

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I have a Arc 1222 with a 16TB (raw) array on it.

I can boot my unraid on that box and see if it sees the array.

not start it.. that would take forever to restore

I am in the middle of backing it up to an unraid box now. it will prolly take a day or 2 still before I can test it..


I also have a LSI with 16 drives on it... Im not so sure if i want to test that array... it has minimal backup right now.

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14TB cache drive anyone?





Since I only had the Free unraid on that drive, I could not test it as a cache drive, only parity... it should work.


I did not start the array. i sort of wanted my data. but it looks like you could use a massive raid for a cache drive.... or a drive outside the array.


By thinking outside the box, It makes me think that unRAID is a little more powerful then I thought.


I was planning on getting a new 7200 rpm 3tb drive for parity. maybe ill just toss 2 of my old 1.5TB 7200's in raid0

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....However, I don't understand why you would want to use unRAID if you are already using another form of RAID.





Very easy answer ... but i am new as i told, mabye an error in my brain :)


Today we can use 20 drives as storage, 1 cache, 1 parity. 20x3TB= 60TB usable.

Lets think about ... 4 Drives Raid 5 = 6 TB usable, if visible as a single drive to unraid -> 20x raidset 6TB = 120TB usable. Sure - you have to create 4x3TB Raid 5 parity too ...


If one drive fails - raid 5 "hardware" recovery, unraid will not notice it. 2 drives of same raidset failure -> raidset rebuild, calculating new parity via unraid.


Where is my error ? Performance shouldnt be bad as well ... the "single" drive will have much more io and transfer speed.

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There are so many ways to do the same thing. In the end, it's all personal preference. I just see small RAID5 arrays combined into a larger unRAID array as inefficient use of the storage.


I do think you mean 3 x 3T RAID5 = 6T because 4 x 3T RAID5 = 9T.



3 x 3T disks = 6T in a RAID5 array.

You use 21 such arrays in an unRAID box = 120T of storage with the parity.

The array uses 63 drives.

Can theoretically recover from up to 21 simultaneous drive failures.



21 x 3T = 57T in a RAID6 array.

3 such RAID6 arrays = 171T of storage.

63 drives total.

Can theoretically recover from up to 6 simultaneous drive failures.



11 x 3T = 27T in a RAID6 array.

8 x 3T = 18T in a RAID6 array.

5 of the first and one of the second = 153T of storage.

63 drives total.

Can theoretically recover from up to 12 simultaneous drive failures.



So, how much storage vs how much redundancy do you want? At some point, you have to trade the cost of redundancy for a true backup.




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