Originally Posted by macks
I believe the long initialization with flexraid is when you add a full drive.
Here is what I have learned on the matter.
If your making a simple flexraid array with empty drives it takes almost no time. Example:
4 HDD's, 3 storage and 1 Parity all empty. 3TB each. Would give 9TB usable space.
If all drives empty it takes no time at all.
If your making the same 4 HDD array but 3 of the storage HDD's are full it takes about 10 hours to do it. Put it on a night and it's should be done in the morning.
Flexraid speed it tells you is based on the speed of the slowest drive in your array. Usually for me it's a 2TB green drive and about 85MB/sec
As explained in the thread I had on the subject the reality is it's processing all your HDD and reading at the same time. So it's really reading at 85MB/sec x 3 or there abouts. Meaning it is computing data at about 250MB/sec+ which is why it takes much less time than I was figuring it to take initially.
I did a 20TB array in the same time I did a 9TB array. That made no sense to me. But here is how it works.
I did 6 HDD's of 3TB each for 18TB and then one 2TB green drive. Used a 3TB green drive as my parity (only mention green drives because they are slow giving a worst possible case scenario)
It was reading basically at 7 x 85MB/sec = 595MB/sec
So in reality it takes only as long as it takes to read all the data from your most full or slowest drive- regardless if you have more or less data.
That is why 20TB @ about 595MB/sec takes about the same time as 9TB and only 250MB/sec. In reality it's the same process simultaneously from all drives. reading and computing parity data.
On any modern CPU the CPU or computation process is not the bottle neck. It is the speed of the HDD's. So the time it will take depends on the speed your HDD can be read, and also how much data needs to be read (how full your drives are)
The amount of time it will take to read all data from your HDD is how long it takes. Since it reads them all at the same time, whichever drive is the slowest/most full is the time it takes.
10 hours to initialize 20TB worth of full drives is really actually pretty good performance when you consider what your doing.
I understand the benefit of the new NZFS is going to be much less time though.