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CD1

How protected is my data

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Hello 

 

I understand that unRaid is not a raid (as it is in the name) so how protected is my data encase of a drive failure?

 

I know there is a parity drive but say a disk fails and can no longer be read even by removing it and plugging it into another computer will I still be able to recover the data that was lost from that drive?

 

Also I have seen on the wiki that dual parity is not a copy of the first parity drive (like in raid 6) so what happens if one of the parity drive fails?   

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Posted (edited)

A parity drive protects you against a single drive failure. If a drive fails, plug a new drive in, and the new drive will get rebuilt with the data that was on the failed drive.

If the parity drive fails, then you plug a new drive in, and parity will be rebuilt. A parity drive is not a copy of any one drive. It represents what is stored across all drives, and thus allows any single drive to be lost and replaced.

You can have multiple parity drive to protect against multiple concurrent drive failures.

Edited by Nepherim

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1 hour ago, CD1 said:

unRaid is not a raid

True.  Once of unRaid's best points.  If you're running say RAID-5 and 2 drives drop dead, then you've lost all of your files permanently.  If running unRaid (and a single parity) and you lose 2 drives at the same time, your worst case scenario is only losing a fraction of your files.

 

I can never understand the mentality behind RAID that seems to think that it's better to lose everything than lose some in worst case scenarios.

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2 hours ago, Nepherim said:

A parity drive protects you against a single drive failure. If a drive fails, plug a new drive in, and the new drive will get rebuilt with the data that was on the failed drive.

If the parity drive fails, then you plug a new drive in, and parity will be rebuilt. A parity drive is not a copy of any one drive. It represents what is stored across all drives, and thus allows any single drive to be lost and replaced.

You can have multiple parity drive to protect against multiple concurrent drive failures.

 

1 hour ago, Squid said:

True.  Once of unRaid's best points.  If you're running say RAID-5 and 2 drives drop dead, then you've lost all of your files permanently.  If running unRaid (and a single parity) and you lose 2 drives at the same time, your worst case scenario is only losing a fraction of your files.

 

I can never understand the mentality behind RAID that seems to think that it's better to lose everything than lose some in worst case scenarios.

Thanks for the reply but has any one ever experienced a complete drive failure and if they had any issues recovering their data? 

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Yeah, it happens.  I have terrible luck with WD drives and have more than 1 drop dead.  Rebuild onto the replacement no problems.

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32 minutes ago, CD1 said:

 

Thanks for the reply but has any one ever experienced a complete drive failure and if they had any issues recovering their data? 

Yes. I'm replacing a WD drive right now that had failed. So far no issues, but recovery is underway.

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28 minutes ago, Squid said:

Yeah, it happens.  I have terrible luck with WD drives and have more than 1 drop dead.  Rebuild onto the replacement no problems.

 

1 minute ago, Nepherim said:

Yes. I'm replacing a WD drive right now that had failed. So far no issues, but recovery is underway.

Thanks guys, I am starting to see a pattern with WD drives :D

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Just now, CD1 said:

Thanks guys, I am starting to see a pattern with WD drives :D

To be brutally honest though, I'm a lone wolf around here with regards to my impressions of the quality of WD drives.  I wouldn't install one again if someone paid me to do that.  But, many people will say the same thing about Seagates.  Its the whole GM vs Ford argument.

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Posted (edited)
7 hours ago, CD1 said:

Thanks for the reply but has any one ever experienced a complete drive failure and if they had any issues recovering their data?

I'm using Unraid since 2008 I think. I had to replace many drives in all these years. Not only failed drives need a replacement. Think about the replacement of smaller disks by new bigger disks. I did never count, but it must be dozens here. Removing the old drive and adding the new drive was all I had to do. Never experienced data loss.

 

BUT, once I had a lose SATA cable. During a disk replacement 1400 errors did lead to wrong data on one disk. So, always double check your hardware, especially disk cables.

 

Edited by hawihoney

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6 hours ago, CD1 said:

 

Thanks guys, I am starting to see a pattern with WD drives :D

I will continue to use WD drives. They have been very reliable for me, despite this occurrence. Also, all this is anecdotal. You need to look at large volumes of drives to get an idea of reliability. That's not me, o you, that's orgs who use them all the time.

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16 hours ago, Nepherim said:

Yes. I'm replacing a WD drive right now that had failed. So far no issues, but recovery is underway.

Just a quick follow-up. Failed drive was replaced with a new drive, all data got loaded back onto it, and everything is back up and running. No data loss.

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I was thinking the same thing. I have 2 x 10 and 2 x 8. 1 of my 10tb is a parity drive(have another one ready for double parity)
But the total size doesnt add up to me. Its giving me 26Tb(~23tb useable) atm but i only have a 10tb parity space. Am i missing something? or something i have not selected? i would have thought with the disk config i have would be around an 18tb  array.

 

Loving unraid btw.. have moved off 2 Synologies to my old gaming computer (x99). Shits all over DSM
image.thumb.png.f4f7d77502e4d4b2c712ea6509d50c24.png

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Calculation is correct.  You have 26TB (10 + 8 + 8 )of storage space available.  The 10TB parity drive can (in conjunction with other drives) rebuild any data drive that suffers a failure.

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1 hour ago, ocexperts said:

i only have a 10tb parity space. Am i missing something?

You are probably missing how parity works. Parity is basically the same concept wherever it is used in computers and communication. Parity is just an extra bit that allows a missing bit to be calculated from all the other bits. The parity disk allows a missing disk to be rebuilt from parity disk PLUS ALL the other disks.

 

Parity isn't complicated, and if you understand it a lot about how Unraid operates makes more sense. Here is the wiki on parity:

 

https://wiki.unraid.net/UnRAID_6/Overview#Parity-Protected_Array

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Posted (edited)

was searching community i guess i should have looked at the wiki as that explains it perfectly!
I am used to enterprise raid and work daily on EMC SAN arrays which is very different.
thank you both for the quick reply.

Edited by ocexperts

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10 hours ago, ocexperts said:

I am used to enterprise raid

If it has parity then it is basically the same concept. An extra bit that allows a missing bit to be calculated from all the other bits.

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Since nobody has yet outlined the core tenet around here, I’ll add for completeness;

 

parity is not backup

 

parity is excellent protection against drive failure, and (usually) makes data recovery or drive swaps a breeze. However, consider that in the case of a failed drive, your data is unprotected during a rebuild, just at the point where your system is under most stress with all drives in simultaneous use. What if another drive fails at that point? You will likely lose data on that drive.

 

you should always have a separate backup of critical data stored on your array. Sure, you can re-rip your media, but what about the family photos? 

 

It happened me just a few few weeks ago. My parity failed, and just as parity rebuild was starting to a new drive, another disk went down. I was super lucky that, while the disk wouldn’t add to the array, I could mount it outside the array and recover all the data. I managed to copy it to other drives, then back to an array disk before starting the whole thing up again and allowing parity calculate.

 

not a pleasant experience, but a testament to the flexibility of unRAID that I could get that data of an otherwise failed disk (it was an unfixable XFS input/output error on the second failed disk).

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No expert here. But i feel that in a lot of cases unRAID can find a failing drive, or bad cable.

And it will red ball your drive. failed. But in my opinion alot of times you can do exactly like you did and read your data externally.

I have pulled a drive in the past. Read it externally. Shrank my array till i picked up a new drive and then added it back.

What is nice is even a failed rebuild from parity is not a total loss. one read or write error and it fails. disk may still be usable enough to recover data wit no 

special tools. 

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