FrozenGamer Posted February 28, 2018 Posted February 28, 2018 I would like to do this (and add another 8tb for storage or 2 more for storage as well). I assume that i can pull the 2 existing parity drives and then put in 2 8tb and let it build the parity. Can i put all 4 drives in at once? And what is the advised way to do this with least risk to data? Looking at unraid documentation it says do one drive at a time for multiple parity drive changes and i read that parity drives can be different sizes. Does that mean i could have 1 8tb and 6tb for parity and start introducing 8tb drives to the array for storage? I have 22 drives in my array sized 4 to 6tb at the moment.
trurl Posted February 28, 2018 Posted February 28, 2018 Parity drives don't have to be the same size, but no data drive can be larger than either parity drive. I recommend doing one drive at a time. That way your array will still be protected during the whole process. Are you thinking about adding data disks to new slots, or replacing existing data disks with larger disks?
Frank1940 Posted February 28, 2018 Posted February 28, 2018 Agree with @trurl about the size of parity drives. I personally, would first run a non-correcting parity check and make sure that there are not any errors. (If you find an error, stop and figure why.) Then get a printout of the current drive array assignments just for peace of mind. Then I would replace only one of the parity drives at a time. That way would would always be single disk parity protection for your data. I would personally recycle those old 6TB as new/upgrade data drives but after I had the array up-and-running with the new 8TB parity drives. (Minimizing the number of changes introduced at any one time makes fixing any issues so much simpler!)
FrozenGamer Posted February 28, 2018 Author Posted February 28, 2018 1 hour ago, trurl said: Parity drives don't have to be the same size, but no data drive can be larger than either parity drive. I recommend doing one drive at a time. That way your array will still be protected during the whole process. Are you thinking about adding data disks to new slots, or replacing existing data disks with larger disks? I was planning on additional drives and keeping old for more storage, but i want to understand franks advice first.
FrozenGamer Posted February 28, 2018 Author Posted February 28, 2018 1 hour ago, Frank1940 said: Agree with @trurl about the size of parity drives. I personally, would first run a non-correcting parity check and make sure that there are not any errors. (If you find an error, stop and figure why.) Then get a printout of the current drive array assignments just for peace of mind. Then I would replace only one of the parity drives at a time. That way would would always be single disk parity protection for your data. I would personally recycle those old 6TB as new/upgrade data drives but after I had the array up-and-running with the new 8TB parity drives. (Minimizing the number of changes introduced at any one time makes fixing any issues so much simpler!) So, i am doing the parity check first, as advised then 1 drive at a time, by recycle you mean take the smaller drives out of the array and replace with larger? get rid of 2 4's for an 8 etc?
trurl Posted February 28, 2018 Posted February 28, 2018 32 minutes ago, FrozenGamer said: So, i am doing the parity check first, as advised then 1 drive at a time, by recycle you mean take the smaller drives out of the array and replace with larger? get rid of 2 4's for an 8 etc? I always recommend using fewer larger drives instead of many smaller drives. Fewer points of failure that way. Larger disks are often faster as well.
Frank1940 Posted February 28, 2018 Posted February 28, 2018 1 hour ago, trurl said: I always recommend using fewer larger drives instead of many smaller drives. Fewer points of failure that way. +1 For a statistical look at the problem, see here: https://lime-technology.com/forums/topic/50504-dual-or-single-parity-its-your-choice/
FrozenGamer Posted March 1, 2018 Author Posted March 1, 2018 On 2/28/2018 at 11:29 AM, Frank1940 said: +1 For a statistical look at the problem, see here: https://lime-technology.com/forums/topic/50504-dual-or-single-parity-its-your-choice/ Good Read.... Why does it say that your reliability actually goes down for a period when going from 1 to 2 parity drives? I didn't really understand this sentence. "Adding a second parity drive to an existing array actually increases the probability of given number of drives failing in the same time period!" I assume that what you mean is the activity involved in the writing of parity while reading from all other drives increases odds? Also you might know the answer to this. It is going to take a long time for parity to rebuild on the first new 8tb drive. I assume all "new" parity is being written to the existing/remaining parity drive and that parity is rewritten on the new 8tb undergoing days long parity write? I have sonarr getting a few shows and adding them during this time frame. Just curious on that. Not super important though if you are busy.
Frank1940 Posted March 1, 2018 Posted March 1, 2018 5 minutes ago, FrozenGamer said: Why does it say that your reliability actually goes down for a period when going from 1 to 2 parity drives? I didn't really understand this sentence. "Adding a second parity drive to an existing array actually increases the probability of given number of drives failing in the same time period!" OK-- You are the first person to question me on this. So I reread the statement again and realized that I didn't say in the best possible way . Let us assume that you have an array with 8 data drives and one parity drive. A total of nine drives. You decide to go to dual parity with the array and you add the Parity 2 drive. You now have eight data drives and two parity drives for a total of ten drives. With one additional drive in the reliability calculation, there is actually an increase in the chance of having a drive fail the next month because of that one additional drive. Hence the reliability will be lower. It is necessary to understand that the table is calculated on the number of data drives. But the probability rate calculation includes the required number of parity drives. If you really think about it, the failure of a parity drive is no different then the failure of a data drive. With the failure of the parity drive with single parity, your data is still all there. If a second drive fails, (in this case it will be a data drive) you will lose data. A similar situation exists for dual parity. After both parity drives fail, the loss of another will cause data loss.
FrozenGamer Posted March 1, 2018 Author Posted March 1, 2018 So i have an increased chance of a drive failing but a decreased chance of permanently losing data, if understand correctly? Thanks for always being so helpful in the forums!
pwm Posted March 2, 2018 Posted March 2, 2018 12 hours ago, Frank1940 said: After both parity drives fail, the loss of another will cause data loss. Or maybe better formulated "after any two drives have failed, the loss of another drive will cause data loss." 12 hours ago, FrozenGamer said: So i have an increased chance of a drive failing but a decreased chance of permanently losing data, if understand correctly? Thanks for always being so helpful in the forums! Yes, the number of drives affects the probability of having a drive failure. But two parity drives greatly reduces the probability of data loss from fatal disk failures (the probability of data loss from user errors is still the same). Going from one to two parity drives is a quite big improvement. Going from two to three is an extremely small additional improvement in availability/survivability.
Frank1940 Posted March 2, 2018 Posted March 2, 2018 12 hours ago, FrozenGamer said: So i have an increased chance of a drive failing but a decreased chance of permanently losing data, if understand correctly? Thanks for always being so helpful in the forums! This is very true but as you read the linked thread, realize that while the loss of data through drive failures falls into the region where the other possible environmental (for the lack of a better word) issues become as big a risk for data loss as drive failures. Multiple backups and offsite storage have to be added to the list of things that have to be implemented. And let's not forget the biggest risk of all, the human one-- Operator error, just plain neglect and lack of attention to detail are items to be addressed.
RichardU Posted March 8, 2018 Posted March 8, 2018 On 3/1/2018 at 6:49 PM, FrozenGamer said: So i have an increased chance of a drive failing but a decreased chance of permanently losing data, if understand correctly? Thanks for always being so helpful in the forums! Like flying a plane with two engines which have twice the probability of an engine failure.
FrozenGamer Posted March 8, 2018 Author Posted March 8, 2018 27 minutes ago, RichardU said: Like flying a plane with two engines which have twice the probability of an engine failure. I like 2 engine planes!
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