Hey Guys   

 

Just about to do my first hard drive addition to my server. I'm running 2x1Tb drives at the moment, and I am just about to install the 3rd TB. My understanding regarding this is that it just comes up in devices and you assign it?

 

I'm also wondering, after parity calculations, how much more space will it give me? I've got 50Gb left on my first TB.

 

I still can't get my head around the way that Unraid shares the disks though. My understanding is that it doesn't stripe the drives, it just shares out each drive? I've got user shares enabled, so example; On my current hard drive I have HD Movies, TV and Movies. Does this mean that I'll need to copy some files to the new drive and share out another folder, or will UnRaid organise and copy my files over the two drives for me?

 

I appreciate any help in advance 

Hey Guys   

 

Just about to do my first hard drive addition to my server. I'm running 2x1Tb drives at the moment, and I am just about to install the 3rd TB. My understanding regarding this is that it just comes up in devices and you assign it?

 

Exactly right.  Just stop the array, go to the devices page and assign the new disk to the next disk "slot", then go back to the main page and start the array.  unRAID will go into a mode of clearing the drive.  It will take a while to fill a 1T drive with binary zeros, but that's exactly what it does.  Make sure you don't want to use the array for several hours after you start this process.  Once complete, I believe the drive will show as unformatted, and you will have to format it.   It may automaatically format it, I forget.

 

BEFORE adding your drive, I would suggest performing a parity check on your existing array.  It is a smart safety measure to make sure your array is in good shape before adding a drive.  I can't tell you how many users wished they had done this!  You might also want to run some diagnostic tests (e.g., the smartctl long test) on the new drive to put it through its paces before adding it to your array.

 

I'm also wondering, after parity calculations, how much more space will it give me? I've got 50Gb left on my first TB.

 

You currently have a 1TB array.  Your 1TB parity drive is not usable space.  Once you add a second 1TB drive, you will have 2TB of capacity.  The parity is a one time "investment", and after that the full capacity of each new drive added is available for use.

 

I still can't get my head around the way that Unraid shares the disks though. My understanding is that it doesn't stripe the drives, it just shares out each drive? I've got user shares enabled, so example; On my current hard drive I have HD Movies, TV and Movies. Does this mean that I'll need to copy some files to the new drive and share out another folder, or will UnRaid organise and copy my files over the two drives for me?

 

I am not an expert with user shares - I just use the disk shares.  But unRAID will take files in the same named directories and make it look like one unified file system.  So if you create "HD Movies", "TV", and "Movies" directories on your new disk, files will be combined across the two disks and made to look like three shared filesystems with those three names.  If you try to copy files to a shared filesystem, the files will be copies to one of the two disks (or some to one and some to the other) based on one of two algorithms.  You'll have to read more about it in the unRAID documentation.

 

I appreciate any help in advance 

 

Hope this helps.  Maybe someone with more experience setting up user shares will chime in.

Awesome, thanks for that info. Just a query on this:

 

You currently have a 1TB array.  Your 1TB parity drive is not usable space.  Once you add a second 1TB drive, you will have 2TB of capacity.  The parity is a one time "investment", and after that the full capacity of each new drive added is available for use.

 

How would it be possible for that 1Tb parity to cover the failure of one of say, 6 1Tb drives? Wouldn't each of the drives have to hold some parity information?

 

Cheers 

The key to understanding how unraid works is to understand that the single parity drive does NOT contain a backup of the other drives.  It merely contains the "even or odd" designation of each bit.

 

If there are ten people on my street and one is at risk of randomly forget his phone number, then we could have one person memorize a single number that is the sum of the other phone numbers.  If one person does forget, then you go to "sum guy" and subtract the other nine - voila, you have the missing phone number.  Parity works similarly.  To recover a drive, it polls all drives, both the parity and other data drives to rebuild the missing drive.

 

 

Bill

The key to understanding how unraid works is to understand that the single parity drive does NOT contain a backup of the other drives.  It merely contains the "even or odd" designation of each bit.

 

If there are ten people on my street and one is at risk of randomly forget his phone number, then we could have one person memorize a single number that is the sum of the other phone numbers.  If one person does forget, then you go to "sum guy" and subtract the other nine - voila, you have the missing phone number.  Parity works similarly.  To recover a drive, it polls all drives, both the parity and other data drives to rebuild the missing drive.

 

 

Bill

 

Hey Bill,

 

Thanks for your quick replies! My understanding of RAID 5 etc is that all drives hold a little bit of parity information to help rebuild the failed drive.

 

"To recover a drive, it polls all drives, both the parity and other data drives to rebuild the missing drive."

 

Would mean that disks on UnRaid would do the same thing as RAID 5, in a sense? So some information is stored on each of the drives, as well as the parity. If this is the case, then how can I have full access to the space on my new TB drive? I'm just struggling to figure out how you can have a single 1Tb drive, and have no other drives holding any parity information, and still have redundancy on a 16 drive RAID set! 

 

Thanks for fueling my curiosity!

When a file is read, it is read from one and only one drive.  When a file is written, it writes to the one drive plus parity.  When a drive is recovered, it reads from all drives.  However, it isn't striping in the sense that no data from disk X is on disk Y.

 

 

Bill

For a little help understanding how parity works, see the FAQ at How does parity work?.

 

Also see the Best of the Forums wiki page (Newbie's Corner) for another helpful link.

Cool - thanks for your help guys!

My understanding of RAID 5 etc is that all drives hold a little bit of parity information to help rebuild the failed drive

That's why it's call unRaid... The traditional forms of raid do what's called stripping.... it distributes data and parity across all drives... unRaid has data for a specific file on ONE data drive and it's attendant parity (along with the parity of the data in similar blocks on the other data drives) is on the parity drive.

 

My understanding of RAID 5 etc is that all drives hold a little bit of parity information to help rebuild the failed drive

That's why it's call unRaid...    The traditional forms of raid do what's called stripping.... it distributes data and parity across all drives... unRaid has data for a specific file on ONE data drive and it's attendant parity (along with the parity of the data in similar blocks on the other data drives) is on the parity drive.

 

Like RAID4 without striping.  Instead of having one huge filesystem striped across multiple drives.

You have file systems confined to each drive. Data blocks from each filesystem/drive are used to build the coordinating parity block.