Question Raid 5 in a NAS

Colin_52

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Can someone help me out?

I need to upgrade my media storage. I've chosen for a QNAP TS-431X-2G with Seagate IronWolf 8TB NAS hdd. I need something that is as close to 100% as possible. I've done some research, and Raid 5 seems to be the best for me.
My understanding is in Raid 5, 1 hdd is used as a back up (parity).
A couple of questions:
1. Can i can buy 2 hdd's to begin with it, both 8tb, and run raid 5, then at a later date add another hdd seamlessly so the raid is now backing up 2x8tb? Trying to save on the initial cost.
2, Does raid 5 mean if anyone of the other hdd's fail, i can replace the hdd and not loose the content?

thanks
 

USAFRet

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(I have a QNAP TS-453a)

RAID 5 requires 3 drives minimum.
Starting with 1 drive and adding 2 later for this RAID 5 requires a FULL format of all drives. You can't just put in the 2 new ones and say "Be a RAID 5". Full format.

RAID 5 is NOT recommended for large drives. The rebuild time will be hours/days.
3x 8TB drives in RAID 5 = 16GB usable space. Fill it up with say 10GB. Replacing a drive and recovering will be "Click - come back tomorrow"

It is ONLY for physical drive fail. Does nothing for all the other, more common, forms of data loss.
 

Colin_52

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Hi

Not sure I clearly explained what I meant. I'm only using this to store movies & music. currently my external hdd tower is on its way out. I have 8tb of movies on it.

I want something that lasts or at least can be replaced without loosing the media.
my thinking behind using raid 5 was to have 3x8tb - 24tb disks for storage, and 1x 8tb for parity. Being movies, I can replace individual movies just not a whole disk with 8tb on it.

So once I transfer all 8tb of data over to my new set up, it will be a case of once or twice a month adding a new movie to my collection.

what raid would you suggest to go for?
 

ex_bubblehead

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You need to read up on what RAID 5 actually is and how it works. RAID 5 requires no less than 3 physical drives. Parity is spread out equally among all the drives, there is no single parity drive. This parity requires space equivalent to 1 of the 3 drives. Total space available will be equal to 2 drives (minus formatting).
 

USAFRet

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3x 8TB + RAID 5 = 16TB usable space, in a single volume.
The space of 1 drive is used for parity. Not the 'actual drive', just its space.
https://en.wikipedia.org/wiki/Standard_RAID_levels#RAID_5

Data is spread across all 3 drives.
Yes, one drive can fail, while retaining all data. You remove the dead drive, put in a new one. Then wait for the entire array to rebuild itself.
With 8TB of actual data, that rebuild time = "Come back tomorrow". The array/volume is unusable until it completes.

Yes, I tested this with my QNAP.
Originally, it had 4x 3TB drives. RAID 5. 9TB aarray size. Approx 6TB data in the array.
Replacing those with 4x 4TB drives.
Power off, take out a 3TB add a 4TB. Rebuild.
That rebuild took approx 7 hours
Repeat for the other drives.

That drive swap took 3 days.
I did it that way mostly as a test to see how the QNAP acted in the event of a dead drive.

What would I do with that QNAP?

2 drives in a JBOD volume, to hold the Movie lib
1 drive in a single volume to hold the Music lib
1 drive (10-12-14TB?) to hold an actual backup of the others.

The QNAP OS will do a backup of your Movie and Music folders to the 4th drive, on whatever schedule you want.
That IS an actual second copy. An individual files can be retrieved.
 

Colin_52

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Thanks for the replies guys.

I did research it but obviously networking is not my strong point. computers was my thing when i was younger but that fizzled out.. thats why i need your help lol.. :D

I understand that parity is stored across all hdd's. Correct me if i'm wrong, but i thought parity requires a total storage capacity of a single drive? So if i have 4x8tb hdd's i'll loose 8tb of storage through parity, or am i wrong?

if all 4 drives are 8tb....
2 drives at JBOD = 16tb capacity
1 drive music = 8tb capacity
1 drive back up,
How can i back up potentially 24TB into a single 8tb?

regards
 

USAFRet

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8+8+8+8 + RAID 5 = 24TB potential size of the array.

The size of your backup space will have to adjust to the size of your actual data.
Just because the RAID array can hold 24TB, does not mean you have 24TB of actual data in there.
 
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Colin_52

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that was just as a maximum. at the moment i'm up to about 7.5tb in movies.
I'm just trying to future proof it and know what i can potentially have..

its shame you can't start with 3 hdd's and add a 4th at a later date in a year or so without loosing the data. This would save a few $$ on the initial cost...
 

USAFRet

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that was just as a maximum. at the moment i'm up to about 7.5tb in movies.
I'm just trying to future proof it and know what i can potentially have..

its shame you can't start with 3 hdd's and add a 4th at a later date in a year or so without loosing the data. This would save a few $$ on the initial cost...
You can't start with 2 drives, add a 3rd, and have it be a new RAID 5.
You can add a 4th drive to an already established 3 drive RAID 5, without losing data in the existing array. Any data on the new 4th will be wiped out.

In the QNAP user manual, under RAID Management, subsection "Add a drive".

https://forum.qnap.com/viewtopic.php?t=90001

Of course, I wouldn't do this without a FULL second copy of all data in the array. Just in case.

When I expanded mine from 4x 3TB to 4x 4TB I had a known good backup of all data. Just in case.
 

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