8TB drive turns into 6.9TB? Where is my .5TB?

[dssguy1]

Ok so I have a Freenas setup and am just starting to experiment. I bought a couple of the 8TB Mybooks that had Hitachi He8 drives in them and decided to use them just to hold media files that I don't care if I lose from hard drive failure. I have large 5 and 7 disk arrays that I am using for my important files so don't worry about that!

So I created a single drive volume and happily started filling it with Blu-Ray copies. Only when it was almost full did I realize it was only 6.9TB big. I know I won't get my whole 8TB once formatted but I thought I should be closer to 7.4TB? Where is my math going wrong?

Also, I am getting warning about being more than 80% full on this drive. It is just a media storage drive, does this even matter? Is there a way to turn that warning off on this drive?

 

[depasseg]

1TB = .9TiB So right off the bat the Marketing folks stole 10% of what you thought you had. So then you are at 7.2 TiB and then there is metadata/overhead which probably gets you a little closer to 7. Bidule0hm has a great ZFS storage calculator.

 

[dssguy1]

I thought it was .93 marketing bastard factor. So 7.44TB. I did a stripe single drive volume, is that still considered ZFS and ate .44TB in overhead?

If so, geeze!

 

[dssguy1]

Ok so I have seen that Raid calculator before and it says with 8TB I should have 7.276 TiB and overhead is .116TB. Seems like I should show something closer to 7.16TB for full capacity. Why am I sitting at 7.0TiB?

I know, I'm whining about .16TB but add the 20% freespace I am supposed to keep and this 8TB drive really gets a kick in the junk on usable space.

Can somebody comment on the need to keep 20% free space on a single striped drive for large Media files?

 

[Robert Trevellyan]

Can somebody comment on the need to keep 20% free space on a single striped drive for large Media files?

Only in a general sense. The warning is designed to give you time to take action before you reach 90% (I think), at which point the algorithm ZFS uses to allocate blocks changes to something much slower. If you're treating this as WORM storage, and you keep it below 90%, you might be OK. Try unchecking the box in the popup that appears when you click the warning light in the GUI.

 

[Bidule0hm]

There's one type of overhead missing (didn't have the time to add it) so the 0.16 TiB probably come from here.

 

[Steve Brown]

Do you have snapshots?

 

[dssguy1]

No snapshots.