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Billy Pilgrim

What is the purpose of RAID 1

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1 minute ago, Billy Pilgrim said:

What is the purpose of RAID 1 if it doesn't provide a good backup?

who said it doesnt?

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Redundancy, so when a disk fails you don't lose everything and have time to migrate it to another system.


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Just now, ki8aras said:

who said it doesnt?

RAID should NEVER be considered a backup. A backup should be storing the files off the system onto some other system, media, etc. so if the whole thing dies you can still restore your files.


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4 minutes ago, Billy Pilgrim said:

I hear that the problem with it is that it doesn't protect against data corruption.

Protecting against corruption is one of the primary reasons for RAID to exist in the first place.


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1 minute ago, WereCatf said:

Protecting against corruption is one of the primary reasons for RAID to exist in the first place.

Isn't raid mainly for drive failure? Normally raid has no idea if files are corrupted and can't correct corrupted files. Corruption normally also happends at the software or filesystem level.

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Posted · Original PosterOP
Just now, Electronics Wizardy said:

Isn't raid mainly for drive failure? Normally raid has no idea if files are corrupted and can't correct corrupted files. Corruption normally also happends at the software or filesystem level.

Thats what I was thinking.

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3 minutes ago, Electronics Wizardy said:

Isn't raid mainly for drive failure? Normally raid has no idea if files are corrupted and can't correct corrupted files. Corruption normally also happends at the software or filesystem level.

Of course RAID knows if there's corruption. The difference is: it can't protect if you write corrupted files to it, because the corruption has happened before the file was even written to the RAID. If you write uncorrupted files to a RAID, it does protect the files from bad sectors or bitrot or whatnot the disk that would otherwise corrupt the file. RAID doesn't need to know what filesystem there is or anything, it operates at a lower level and filesystem is on top of it.


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1 minute ago, Electronics Wizardy said:

Isn't raid mainly for drive failure? Normally raid has no idea if files are corrupted and can't correct corrupted files. Corruption normally also happends at the software or filesystem level.

This, RAID1 just clones files from a drive to another, if a drive fails the other can be useful to keep the system running


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1 minute ago, WereCatf said:

Of course RAID knows if there's corruption. The difference is: it can't protect if you write corrupted files to it because the corruption has happened before it got written to the RAID. It can protect you if there are bad sectors or bitrot or whatnot the disk, corrupting the file.

how would raid know there is corruption? For traditional raid 1, there is no checksums to it has no idea if the data being read is the same as being written. It will just pull data from one drive and give it to you.

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3 minutes ago, Electronics Wizardy said:

how would raid know there is corruption? For traditional raid 1, there is no checksums to it has no idea if the data being read is the same as being written. It will just pull data from one drive and give it to you.

No, RAID1 is a mirrored RAID; when you read from it, it reads from multiple drives in the array and compares them to see that they're identical. You're thinking of RAID0, which is just striped.


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1 minute ago, WereCatf said:

No, RAID1 is a mirrored RAID; when you read from it, it reads from multiple drives in the array and compares them to see that they're identical. You're thinking of RAID0, which is just striped.

Have you seen this

 

Traditional raid is dumb, with raid 1 if there is bitrot, there is no way of knowing if data is correct. You can compare the data on the 2 drives, but if its different you have no idea what is correct.

 

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22 minutes ago, Billy Pilgrim said:

What is the purpose of RAID 1 if it doesn't provide a good backup?

To protect you against drive failure in high availability systems.  If you are running something that is so important and sensitive you can't afford for it to go down ever, you can use RAID 1 (or 5 or 6, etc.) to ensure you can lose a drive, and then swap it out for a new one live, while the system keeps running without a hitch through it all.

 

For the normal user, this is completely unnecessary.  As explained below, RAID does not replace a backup, it can only supplement one, and at home, if you lose a drive, you can afford the few hours to recover from said backup, so it's just extra cost for no real benefit.

20 minutes ago, ki8aras said:

who said it doesnt?

Everyone who knows how it works.  A separate backup protects you against a lot of things that RAID will not: accidental file deletion, theft/fire/other disasters, ransomware, and even failure of the array itself, to list a few.

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