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Why am I losing so much disk space with Linux (vs Windows)?

1022 Views 4 Replies 5 Participants Last post by  georwell
I'm a relative newbie with Linux, but fairly advanced otherwise. I previously had my media server setup with a hardware RAID card (the LSI Logic Megaraid i4) on Windows XP using Maxtor 300GB ATA drives. I recently filled my array, and have been playing around with Linux software RAID as a possible platform for my server.

The "300GB" Maxtors have a raw capacity of 283 GB. With hardware RAID under Windows XP, an NTFS formatted 7-disk RAID-5 array yielded a storage capacity of 1.67 TB. (which amounts to ~ 278 GB /disk) Also a non-raided drive yields the same 278 GB size after NTFS formatting.

Using Fedora Core 3, I created a 4-disk RAID-5 array using ext3 file system with the same 300 GB Maxtor drives. I was shocked to see my available capacity was only 783 GB (261 GB/disk). I installed the root and swap partitions on a separate system disk, so there is no usage of the array by the system. "df -h" indicates a size of 838 GB for the array, but with 1% usage and only 783 GB available? What happened to those 55 GB? Does the ext3 file system eat that much space? I was planning on running a 12-disk array ultimately, but with this difference in capacity, it is almost worth buying Windows Server 2003 and using its software RAID instead...

Any suggestions?
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Does the ext3 file system eat that much space?
My guess is your ext3 filesystem could be finetuned.

See if this helps:

Scroll down to the etx3 praragraph.
I think nuthead is correct.

A couple things which could effect available size are journal size and reserved block percentage.

I would let the journal size default, but if this filesystem is strictly for storing media, then

you may want to set the reserved block percentage (amount of space reserved for root when

the disk reached out of space condition) to zero. The default is 5%, so, getting that 5% back

would get you from 263GB/0.95 = 276GB. That's almost all the way back from the 278GB you

see on NTFS.

Normally, you want that 5% so that if the disk hits an out of space condition, root processes

still have some headroom and aren't choking. (If root is unable to write, things tend to break

in spectacular and unusual ways.) But, in this case, if the entire filesystem will only contain

your media files, then there's no reason to throw away that 5%.

Hope that helps,

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Some of the space will also be used for Inodes. If you have lots of large files, the number of inodes can be reduced.
Perhaps you should consider a different file system then ext3? XFS or JFS are both good at handling large files. JFS also deletes them instantly. :)
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