[SOLVED] Install Old Parity Drive and Trust It

[Christopher]

My system currently doesn't have a parity drive. I want to install an old parity drive and have unraid trust it. When I start the array with the old parity drive I want this think everything is normal.

 

Can someone point me to the link for this procedure?

 

Thanks,

Christopher

[Squid]

My system currently doesn't have a parity drive. I want to install an old parity drive and have unraid trust it. When I start the array with the old parity drive I want this think everything is normal.

 

Can someone point me to the link for this procedure?

 

Thanks,

Christopher

If its an old parity drive, why would you want unRaid to trust it?  The data on it is going to be invalid.  You're going to be better off not trusting it and having unRaid build the parity info on it.

[SSD]

One big difference between RAID5 and unRaid is that with RAID5, the redundancy is always correct. With unRaid, a user has the power to slap in a parity drive, tell unRaid to trust it, and then the array work for months or years with no data corruption and appears all is great. Until a drive fails and unRaid's simulation of it is crap. Unless you run a parity check, you would never be able to tell that parity is totally useless!

 

Be careful trusting parity! As suggested, rebuilding it might be smarter than trusting it. But if you think the old parity is close, trusting it should be fine so long as you immediately do a correcting parity check and allow it to correct some of the parity blocks. This could be faster than a complete rebuild.

[Christopher]

One big difference between RAID5 and unRaid is that with RAID5, the redundancy is always correct. With unRaid, a user has the power to slap in a parity drive, tell unRaid to trust it, and then the array work for months or years with no data corruption and appears all is great. Until a drive fails and unRaid's simulation of it is crap. Unless you run a parity check, you would never be able to tell that parity is totally useless!

 

Be careful trusting parity! As suggested, rebuilding it might be smarter than trusting it. But if you think the old parity is close, trusting it should be fine so long as you immediately do a correcting parity check and allow it to correct some of the parity blocks. This could be faster than a complete rebuild.

 

Thanks for the info bjp999!

 

If its an old parity drive, why would you want unRaid to trust it?  The data on it is going to be invalid.  You're going to be better off not trusting it and having unRaid build the parity info on it.

 

Here's the reason why I want to do this:

 

[*]Initial state of my server was perfect. I had just done a parity check and all was well.

[*]I upgraded my parity drive from 4GB to 5GB, Unraid started building parity.

[*]In the morning I saw disk13 was redballed and parity build did not complete. Nothing has been copied/deleted/edited to the server since.

 

 

I did not trust my old parity because events happened between steps 1 and 2 that wasn't sure about and I don't recall the details of. So I used reiserfsck to recover disk13 data and it restored about 2/3 of it. I copied the restored data to a local disk on my PC. Now I want to try to rebuild disk13 from my old parity. I realize that it the parity info might be invalid. But I wanted to give it a shot.

 

Once I rebuild it I want to do an md5 comparision with the reiserfsck recovered data.

 

Can you point me to the procedure?

 

Thanks,

Christopher

 

 

 

 

[SSD]

Too late, but in my sig is a link to a best practice on upgrading parity that would have handled this situation.

 

I think you are in the right track with your trust parity. You have to have the redballed disk (or a surrogate) in place when the new config is done. Once the array is configured you can remove it to force the rebuild. I actually like to remove the disk and see the real-time simulating as a preview of what the rebuild will build.

 

Some have reported that trusting parity kicks off a parity check. I don't remember that happening when I did it last but not sure. I'd be prepared to stop the parity check as quick as possible if it happens. I hate that unRaid kicks off such checks without giving the knowledgeable user a means to prevent it.

[Christopher]

The parity drive I want to use to restore disk13(3TB) is 4TB. I would like to replace disk13(3TB) with a new drive but my only spares are 5TB. Is there anyway I can make the 5TB appear to be 4TB or 3TB? This is just temporary so I can rebuilt disk13.

 

Thanks,

Christopher

[SSD]

The parity drive I want to use to restore disk13(3TB) is 4TB. I would like to replace disk13(3TB) with a new drive but my only spares are 5TB. Is there anyway I can make the 5TB appear to be 4TB or 3TB? This is just temporary so I can rebuilt disk13.

 

Thanks,

Christopher

 

"Any way" sounds like a challenge. There is a way to create an HPA on a disk to make it appear smaller. You might look HERE for how to do it. Before unRAID supported drives greater than 2.2T, I was able to create an HPA and make a 3T appear as just under the threshold. This allowed me to use a recently purchased 3T drives purposefully until the large drive support was implemented. When it was I was able to transfer the data off of it, remove the HPA, and they copy the data back to it. It is a rather blunt instrument but should work. Some controllers do not allow the HPA to be installed or removed - but normally motherboard ports do.

 

I do not know of another way. People have created 2nd partitions manually, but I think that only works on the cache drive. Might give some time for others to review and offer suggestions. WeeboTech would be a good one to ask - might want to send him a PM and point him to this thread.

[Christopher]

A Friend let me borrow a smaller drive and I was able to complete the process. Thanks for you help!