Sidebar Sidebar
Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.

HDD available capacity : a beginner question for 1TB drives RAID 1

M

MCHR

macrumors regular
Original poster
Mar 13, 2009
152
1
After doing a lengthy search (and finding some relevant information), I wanted to ask a specific question about final volume capacity in larger sized drives.

Now that I understand the reason between the 'advertised' size and what we see on our Disc Utilities, I now know that a 1TB drive shows up as a 931GB volume. While I don't want to give away that 69GB capacity, I guess I'm good with that.

My specific question is that I've just installed two WD RE3 1TB drives as a RAID 1 in a Synology NAS. Install went very easily. What I am now seeing as an available capacity is 912GB. A full 19GB less than the 931. I also understand that the OS creates folders, and future room for updates. But 19GB seems like a lot. At least to me.

The Synology OS needed 300MB of room, and shows in the DSM panel.

So, my elementary question is. . . . . does this seem correct? I have heard that larger capacity drives end up less than 93% of their advertised capacity. If anyone has any pointers or information, I'd appreciate the education.

Otherwise, it seems like something may be wrong with the firmware etc in the drives themselves. Thanks for any info.
 
I'm not sure about your Synology NAS, but just out of curiosity, which OS are you using that your hard drives still show their "real" size instead of the advertised?
 
Transporteur said:
I'm not sure about your Synology NAS, but just out of curiosity, which OS are you using that your hard drives still show their "real" size instead of the advertised?
Click to expand...


Those figures were shown in the Synology DSM (Disc Station Manager). Where the volume shows 931GB, and the available capacity shows 912GB. It also shows the space used for the DSM software is 299MB.

So, in my (uneducated) mind that's a lot of un-explained capacity.
 
That was what I thought. I've also posted on the Synology forum to see what others are seeing in real world installs.

The Synology help desk indicates that 19GB is excessive and are looking into it. I've also contacted WD to see if formatting the RE drives uses more room, though I doubt it.
 
Manufacturers like to say 1TB = 1,000,000,000,000 bytes which is base 10. In reality 1TB = 1,099,511,627,776 bytes because computers are in binary (base 2); so if you do the conversion backwards from 1,000,000,000,000 bytes back, it should be 0.909494702TB or 931.322575GB.

So you didn't lose any capacity; manufacturers use base 10 to make their drives looks big while computers read and calculate it in binary and do the conversion that way which nets a "smaller" number.

Also Apple changed Snow Leopard (10.6) to display the figures in base 10 to match what the manufacturers are doing.
 
You must log in or register to reply here.
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.
Top Bottom
Back