Greetings, hopefully an easy question. My array consists of 8 disks total. 4x of them are 3TB and 4x of them are 2TB. I just received my new drives in the mail and I'll be upgrading the last of the 2TB drives to 3TB.

 

Last year I did this for my 1TB drives and before I started upgrading anything I ran a parity check. After each individual disk rebuild I also ran a parity check before upgrading the next drive. The parity checks take about a day on my array, so this added an extra 4-5 days onto the whole upgrade process.

 

My questions is, after running that first initial parity check and disabling the mover script so nothing new is added to the array, is it really necessary to run a parity check after upgrading and rebuilding each disk?

That IMO is up to you, if you know that none of your data has been corrupt - it can be done, but you should always try keep a valid parity. You never know when another drive/cable could throw a wrench into your plans - this way you are only dealing with one variable at a time and minimizing any data loss.

It is entirely up to you, but re-constructing onto a new drive writes the entire contents of a drive

BUT DOES NOT READ IT TO ENSURE IT WAS WRITTEN PROPERLY.

 

The only way to know it was written properly is to perform a parity check.  (When it will be read in its entirety)

 

Reconstruction of a  subsequent drive reads the entire set of remaining drives.  However, this is NOT the time to learn of an unreadable sector on the previously replaced drive. (It is too late... you've lost data)

 

If you want to risk it, you can skip the intermediate parity check, but it is a high risk if you do.  You have about a 1 in 8 chance of all 4 of your new hard disks to be error free.

Argh you're right! I was hoping for someone to tell me, "Hey don't worry about it you'll be fine." To be honest, though, I definitely see how minimizing risk making sure I have fresh parity while rebuilding a disk is valuable.

 

Besides, running a preclear on a 3TB drive takes a long time. It's not much less than the time to rebuild a drive and resync parity so I'll just bite the bullet and check parity after every drive rebuild.

 

Thanks for talking me out of doing something dumb guys!

Argh you're right! I was hoping for someone to tell me, "Hey don't worry about it you'll be fine." To be honest, though, I definitely see how minimizing risk making sure I have fresh parity while rebuilding a disk is valuable.

 

Besides, running a preclear on a 3TB drive takes a long time. It's not much less than the time to rebuild a drive and resync parity so I'll just bite the bullet and check parity after every drive rebuild.

 

Thanks for talking me out of doing something dumb guys!

If it makes you feel any better, you are in good company.  I've got 2 new "black-friday-sale" 3TB drives sitting here and another RMA'd drive expected to be delivered to me on Monday.    I've got the same tasks ahead of me replacing 3 smaller drives.

That reminds me, I've got a drive I need to file an RMA for as well. It's definitely worth the careful effort because after this upgrade I'll be set for 2014. Hoping that 4TB drives start coming down in price and late next year I'll scoop up some on a black Friday deal. I'm not extremely interested in growing my array out, but rather up to reduce risk. At least until unRAID supports dual parity (which may or may not ever happen).

 

Thanks for chatting it up with me. Good luck with the upgrades!