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Old 12-15-2007, 07:48 PM   #1
Lommer
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Ext3 Filesystem overhead on a 1TB drive


Hi all, first time poster.
To familiarize myself with linux, I'm setting up a debian box to act as a fileserver for my small business. There's a couple smaller internal physical drives that hold the OS and swap space, and I've bought a 1 TB external disk to hold the files (Western Digital MyBook). After formatting to ext3, "df" reports 870 GB of free space! I think the disk might actually be only 931 GiB due to marketing bs, but that would still leave 60 gigs of overhead which seems like a lot!

Question: Is 60 gigs (6.4%) a normal amount of overhead on an ext3 filesystem? Is there any way to reduce this? Are other linux-compatible filesystems more efficient in terms of disk overhead? How much could I hope to gain by switching to them?

P.S. I understand ReiserFS is supposed to have less overhead, but I can't find any numbers to quantify how much space I'd stand to gain by switching. I'd like to figure out what my optimum solution and then implement it rather than guessing and testing a bunch of different possibilities.
 
Old 12-15-2007, 08:07 PM   #2
bigrigdriver
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6.4% seems a bit excessive. I seem to recall reading that ext3 reserves 3% for system use. You can adjust that figure with the tune2fs utility.
 
Old 12-15-2007, 08:24 PM   #3
Lommer
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Hrm, I actually just ran df, and this is what it outputted. I guess I incorrectly assumed that what the debian GUI reported as free was what df would report. So why the discrepancy between the GUI-reported free space and what's shown here? Is this another 2^30 bytes vs. 10^9 bytes conversion thing? Also, what is taking up 73.352 MB of drive space? The only thing currently on that drive is the empty "lost+found" file.

This was the relevant output of df:

Code:
Filesystem           1K-blocks      Used Available Use% Mounted on

/dev/sdb1            961432072     73352 912520720   1% /media/TBdisk
P.S. What would I do with Tune2fs? I formatted the drive with just default settings (no extra params).
 
Old 12-15-2007, 08:44 PM   #4
HappyTux
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Quote:
Originally Posted by Lommer View Post
Hi all, first time poster.
To familiarize myself with linux, I'm setting up a debian box to act as a fileserver for my small business. There's a couple smaller internal physical drives that hold the OS and swap space, and I've bought a 1 TB external disk to hold the files (Western Digital MyBook). After formatting to ext3, "df" reports 870 GB of free space! I think the disk might actually be only 931 GiB due to marketing bs, but that would still leave 60 gigs of overhead which seems like a lot!

Question: Is 60 gigs (6.4%) a normal amount of overhead on an ext3 filesystem? Is there any way to reduce this? Are other linux-compatible filesystems more efficient in terms of disk overhead? How much could I hope to gain by switching to them?

P.S. I understand ReiserFS is supposed to have less overhead, but I can't find any numbers to quantify how much space I'd stand to gain by switching. I'd like to figure out what my optimum solution and then implement it rather than guessing and testing a bunch of different possibilities.
I did a quick calculation once it is here you can get quite a bit back for even your ext3 by making sure that only 1% is used for the reserve space instead of the default 5% and to answer the original question the 60gb looks about right using ext3 default options.
 
Old 12-15-2007, 09:55 PM   #5
syg00
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On a data drive there is no need to reserve any - just set it to zero. Will reclaim that 5%.
"man tune2fs"; check the "-m" option.
 
Old 12-15-2007, 11:36 PM   #6
Lommer
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Thanks all, after setting the reserved blocks to 0 "df" now gives 961 GB available which is a much more reasonable ~4% overhead. And I think the GUI vs. "df" results are just the GB vs GiB conversion (The GUI uses GiB).

Thanks again for all the prompt help.
 
Old 03-20-2008, 02:12 AM   #7
the_tflk
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I had a somewhat similar situation, ie. wondering about what type of filesystem would be best used on an external 1TB drive.
Anyway, this was helpful to find.
Thanks.
 
Old 03-20-2008, 09:55 AM   #8
H_TeXMeX_H
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I would say something like XFS or JFS. These are the two best journaled filesystems available for linux. It does depend, but most certainly ext3 is not the best in this case.
 
  


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