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[ivan]

One other question, are both drives the same model number?

We have seen a couple of cases where drives that were stated to be the same capacity and put in a RAID 1 array showed up with one drive having unused space.  We tracked the space down to how the drives firmware dealt with the spare sectors used to cover faults in the platter (ID5 on the SMART table).

I don't know if it this in your case and since people generally buy drives in pairs if they are going to setup a RAID array I didn't mention it.  Different SATA speed ratings can cause space discrepancies again because of different drive firmware, this normally doesn't matter if the drives are going into a computer or a JBOD or STANDARD RAID array.

[Matt26]

both hard drives are WD5000AAKS, Caviar Blue models.. both hard drives have a date of March 4, 2010.

[ivan]

Very strange.

You now have two choices, 1) go with what you have or

2) download the WD disk tools and then pull a drive, put it in a USB/SATA caddy or adapter, plug it into the computer with the disk tools loaded then run the full battery of tests.  Save all information then replace the drive in the NAS and then do the same with the other one.  You can then compare the two sets of results for any anomalies which may indicate where the spare space is from.

You have had my people scratching their heads over this.  Yes, we can understand different capacities on different drives and a RAID 1 array will always use the smaller amount - the idea is that both parts of the array are identical.  You said that you think there is 1.5 GB available on each disk, normally that would only happen if you specified an array that was smaller than the full capacity of the disks - we have seen that when a client installed 750GB disks but formatted them as a 500GB RAID 1 array because that was what the old array was.  In other words we are clutching at straws over this.

Another thing my service guy just pointed out you should log in to the webUI, go to 'Management' --> 'Disk Management' and check what is shown there regarding disk capacity.

[Matt26]

update: i decided to do some further RAID testing with other hard drives, to see if the JBOD shows up again and to test some other things.

i set up a new RAID1 with two 80GB WD WD800JD-60LUA0 hard drives.  not sure how to attach screenshots, but during the RAID1 setup i was presented with a "Size Settings" section where you set the size of the RAID1 (72 GB max in this case) and how to handle the remaining space (3 GB); the only options are to leave it unallocated or create a JBOD.  i left it unallocated this time to see what happens- it just creates the RAID1 volume and then under the "Disk Management/Hard Drive Configuration" page there's an option to "Create A New Volume From The Remaining Available Storage Space", which i did, so now i also have a 3 GB JBOD volume.

what's interesting is that the 3 GB unallocated space in this case (with an 80 GB RAID1) appears to be the same as with my earlier 500 GB RAID1 (ie the unallocated space doesn't appear to scale according to the RAID1's size), so i wonder if that 3 GB is set aside by the DNS for some reason?  i don't get it, i can still use this space for storage, so why can't it be added to the RAID1 volume?  i agree, very strange!

[Matt26]

update: i finished my testing and decided to plug in my 2 new (factory sealed, purchased together) WD WD101KFBX 10TB Red Pro hard drives, as these are what i will be using for my "live" NAS.. same thing happened, created RAID1 array with 2GB remaining for JBOD, which i configured.

i guess this is just by design, unless anyone has any thoughts to share that might debunk this conclusion..