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HDD Space problems

E

edday

n00b
Joined
Jun 21, 2003
Messages
22
I setup 2x120gb wd drives on an adaptec 1200a raid controller in raid1 on my freebsd4.9 box today, setup as per the handbook, and shared it using samba 2.2.8a, and noticed that it said the following when i mapped it to my windows machine:
Total space 110gb free 101gb

Now this is a brand new, entirely empty drive, but says it had 9gig in use. The OS runs of a seperate scsi drive.

Is this some sort of overhead from freebsd or samba that i haven't read about?
 
You're seeing two mechanisms eat up that disk space. The first is the typical drive manufacturer accounting for HDD space in base 10, OSes using it in base 2 (i.e. 120GB to Maxtor means 120,000,000,000, 120GB to MS, FreeBSD, etc., means 2^30 * 120, or ~128,849,018,880). The other problem you see is overhead due to limitations in UFS. It's a somewhat older filesystem that can and will eat up a lot of space on large partitions, especially when using small block sizes (<=16k). If you want you can up the block size to 32-64k and reduce that overhead.
 
Yep, he's right on that one. 10 GB gobbled up due partly to the drive manufacture labling the drive as 120GB when its not that exactly.... The manufactures see a GB as 1000 mb.. not 1024 like it really is... such that... 120GB is 120,000,000,000 bytes (or is it bits?). i.e. what you will see in overhead for the drive is....
2.34375%
thus....2.81 GB unaccounted for from the manufacturer.. the rest must be from UFS as Snugglebear pointed out.
 
Software sees a gigabyte as 2^30, which actually works out to be more like 1,073,741,824 bytes. You lose a lot more than just 2-3%, typically it's more like 5-8%, depending on overall size. Filesystem overhead adds another 5-15% depending on which you use and how you configure it. The rule of thumb I've used for years is to figure that the drive you buy will be 10% smaller once you get it up and formatted.

On the side, FreeBSD has other filesystems available, and more in development. Whether they move them into the mainstream/defaults or not is almost a religious issue. I'm a big fan of IBM's JFS and JFS2, which are being ported over. Testing takes forever, though, since you want to be 100% sure your filesystem isn't going to eat your data.
 
ahh exactly the information i was after.

I was expecting the drive to show up as about 110gb, but the 9gig in use was a bit of a shock :)

I'll play with the block sizes and see what i can do.

thanks!
 
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