When I set out to give this a try, my plan was to learn by experimentation.  I didn't realize 3 days would have to pass for my drives to be prepared!  So I figure... I guess I can ask some questions here.

 

1) Parity drive size after a failure:  I realize the parity drive "must" be as large as the largest data drive... but is that an absolute?  Or is that just efficient use of the data drives?  My theoretical situation is so...  I have three 2TB drives.  X number of years down the road, one data drive fails.  At that time, 2TB drives are no longer available so I pick up a 6PB drive because that's the smallest that are available (its pretend).  Now, obviously, if I plop that in place of the failed drive... it is going to be much larger than the parity drive.  Does that mean I'm screwed?  Or I just waste everything over 2TB?  Or???

 

just read the answer here.

 

2) I understand the Free edition has a limit of 3 drives.  Is that 3 drives total, or just 3 drives in the array?  I see mention of cache drives and application drives... do they count?

 

3) Is an application drive necessary for a media server using the Plex plugin?  Or can Plex run in memory (off the flash) as well?

 

 

 

Thanks.

 

- Steven

The Basic (free) version supports 2 drives in the array plus parity.  It does not support a cache drive.

 

And is a cache drive necessary?

And is a cache drive necessary?

 

Certainly not for UnRAID.  I don't use Plex, but I know a lot of folks use the cache drive for an application drive, so you get full-speed writes.    If you use an array drive for your applications (e.g. Plex) then your write speeds are limited to the slower write speed of the parity-protected array [unless, of course, you don't use a parity drive].

 

You'd have a lot more flexibility with a Plus license, which not only allows more drives, but also supports a cache drive.

 

I'm starting to regret my decision to start with unraid.  I wasn't sure if I should do unraid or freenas so I was just going to try one, then the other.  I wish I'd gone the other way round.  This enormous 3 day wait just to start is one reason... being (almost) forced to pay $80 just to see if it'll work...

 

anyway, thanks.

You don't HAVE to buy a license -- it just provides the ability to use a cache drive [bTW, a Plus license isn't $80 ... it's $69]

 

You can set up a free system WITHOUT parity and your write speeds will be the same as if you were using a cache.    That will let you test Plex's performance, etc.    Then you can add a parity drive to see how that impacts the Plex performance, and to provide fault-tolerance.    THEN ... after you've decided whether you want to stay with UnRAID, you can decide whether or not to buy a license.

 

Note that this "... enormous 3 day wait just to start ..." is NOT necessary at all.  You elected to pre-clear the drives -- this is simply a good  TEST of the new drives => something it's a good idea to do with ANY system you elect to use.    You COULD have simply booted, added the drives to the array without assigning a parity drive, and Started the array and after a 3-4 minute formatting process you'd have been ready to go.    But then you wouldn't know whether or not the drives had any "infant mortality" problems.    Then, when you later assigned a parity drive, you'd have to wait a few hours for a parity sync -- you'll still have to do that when you assign a parity drive and Start the array.

 

I thought I read in several places that the preclear takes about as long as not doing a preclear because unRaid does the same thing when you add a drive.  I guess I took it that the benefit of doing preclear was that it means less downtime for the array.  So in my case (no existing array) I thought that meant it really didn't matter if I did preclear or not... I'd be in the same boat (ie. two different ways to get to the same place).  I chose to do it because the step-by-step install guide "strongly recommends" it.  Anyway... you're right that it is of benefit to me (ie. knowing the drives are OK) regardless... so that's fine.

 

I obviously have a lot to learn.  I thought the parity drive was an integral, and necessary, part of this system.  I guess I'm not quite understanding the point of unRaid without it.  However, I *DO* understand your logic, so I'm thankful it can work without parity because it does give flexibility in testing, even if it removes security of data.

 

What I'm saying is.... "thanks".  Your logic is sound, and that's the path I'll take:  install without parity, test, add parity, test, decide.

 

Is "few hours" for the parity sync a loose description?  Can I reasonably expect, say, < 4hrs?  Or is this another process that perhaps takes days?

If you add a drive to a parity-protected array, the drive has to be zeroed (cleared) before it's added, so parity will be preserved in the array.    In this case, pre-clearing does indeed allow it to be added quicker; since if you don't pre-clear it, the array won't be available while the drive is being cleared.

 

But if the array doesn't have a parity disk, it's not necessary to clear the drive -- just format it (which is very quick).

 

How long a parity sync will take depends on the size of your drives, the rotational speed, the areal density, and the details of your system (primarily the disk controller).    If you're using 2TB drives I'd expect ~ 6 hours;  for 3TB ~ 8 hrs.  But that can vary by a couple hours depending on a variety of factors.

 

Cool thanks.

Also you can mount a drive outside the array to use as an application drive (plex drive) and still use the free version of unRAID for your array.  Just add some commands to your go file to create a directory to mount the drive to then mount the application drive to that directory.  A tutorial for plex app drive is here.

Thanks.  Only wish you'd mentioned it earlier

 

I was running into walls.  Everywhere I turned, the solution was to buy a license, but a license, buy a license.  I'd have no problem buying a license once I knew it was going to work.  But it seemed like a catch-22.  Every tutorial or example I could find on my own, regarding plex, made it appear a cache drive was necessary... and you can't have that without a license.  In the end, I asked myself to re-examine why I was looking at unRaid in the first place.  The answer:  as an alternative to FreeNAS because its snooty hardware requirements appeared insane (up to 5GB of ram per TB?  My lowly 4TB needing 20GB of ram?  Yeah... right).  I realized eventually that I could get bye with much less... but I was already on to unRaid.

 

Anyway, for now I'm not doing either.  I've installed Ubuntu and I'll just give that a try for the time being.  If I hit any walls there and decide to look here again... I'll be thankful for your tutorial link.