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I am trying to set up a storage server which has a hardware raid controller and 15x3 TB harddrives. This server is a dedicated server from hetzner.de and I am using the default setup routine (installing an preconfigured image) for setup.

The tool for installing the images does not allow partitions with more than 2TB, so I configured it as followed:

100GB / 
512MB /boot
32GB  swap

My plan was to create another partition when the operating system is installed. After installation, I used gdisk /dev/sda (which is the only hard drive avaiable) to create another partition with the remaining storage. Created it by doing n then choosing partition 5 (1,2,3 are already in use). After writing that partition table and rebooting I formatted the drive using mkfs -t ext4 /dev/sda5. Mounting the drive works, but df -h tells me that 138GB are used on this partition, which is not true. It's empty except for a "lost+found" folder, which is also empty.

Is there something I'm missing or did I do something wrong? I'm just wondering where the 138GB come from. Any tools I can use to know whats going on?

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4 Answers 4

up vote 2 down vote accepted

Thos 138 Gigs are not actually used space but are filesystem overhead. You wouldn't notice them if you were using ext3 since it creates it proportionally to files stored on that partition, ext4 just create it at the begining before any file was created, and it remains constant. Check this wiki for more informations : https://ext4.wiki.kernel.org/index.php/Ext4_Howto

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The maker of the controller should have a bootable utility to allow for correct RAID configuration. The machine may have a utility built into the card that is accessible on bootup. The 138GB could be nothing more then file structure overhead on 42Tb of disk.

On a serious note. 15x3Tb drives sounds like an external storage array. What RAID level you running (RAID5, ect)? Are you using all the available space as one partition? Are any of those hot spares? at least one should be unless you need all the space. EXT4 allows for you to use the full 15 drives but not having a hot spare makes it a serious and inevitable point of failure.

This does not answer your original question but you might want to give us more information to go any further.

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Yes, it's an external storage array. It's using RAID 5 on an hardware raid controller. The controller presents all 15 drives as one logical harddrive. We don't use hot spares (I know we should but it's out of scope right now). –  Sgoettschkes May 21 '12 at 17:58
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Without question you should use LVM - you can put the entire 45T (or some usable subset) into a volume group and then parcel out individual logical volumes as file systems, raw devices for VM's, set up snap shots / mirroring, etc. I have a 12x2TB and 8x500G arrays (the former software RAID the latter hardware) and have been extremely happy with the ability to grow and shrink volumes (assuming the correct filesystems, of course), create mirrors for backup/test, etc. My advice would be to set up your boot / OS drives (RAID-1 generally) and then put the rest into a common group (RAID-6 or RAID-10 depending on requirements) and overlay LVM onto this latter group.

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Thanks for your suggestion. Not my question actually. We use the server as a storage server only and use RAID5, no need for LVM overhead. –  Sgoettschkes May 21 '12 at 17:57
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The 138G is your reserved-blocks-percentage. The default percentage is 5%. I am not sure how much is your usable space out of your 45TB raw space but the 138GB is your 5% of the usable space. If you want less than that. Do the following

 mkfs.ext4 -m 1 /dev/sda5. 

That should take only 1% of the usable space.

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those are not reserved blocks (1% of 45 TB represents much more than 138 GB) –  m0ntassar May 21 '12 at 16:18
    
Read it full. I didn't say what your thinking. –  Chakri May 21 '12 at 16:23
    
he says The 138G is your reserved-blocks-percentage, I said they are not and I gave a sample between () –  m0ntassar May 21 '12 at 16:26
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