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Gullible Jones

Member

Registered: 2004-12-29

Posts: 4,863

Ext3 "fast format"?

When experimenting with Moblin, I noticed that it was able to format a 160 GB ext3 partition in a few seconds. Anyone know what options it uses to do this? Formats of such large partitions usually take several minutes for me.

Ultraman

Member

Registered: 2009-12-24

Posts: 242

Re: Ext3 "fast format"?

Probably has different default settings. I'm guessing it creates less inodes, that's usually the lengthier operation with bigger disks. Inodes get created on a per amount of bytes basis. I believe it defaults to an inode for every 16KB.
If Moblin knows a filesystem is going to hold files that are on average bigger than that it makes sense to increase the inode-ratio (inodes per bytes), which will lower the number inodes that need to be created.
Unused inodes waste space, and could potentially waste system memory as well. So it's plausible they took that into account when setting their filesystem defaults.

If you know you are going to use a disk for files with an average size of at least 1MB, you can try adding " -i 1048576 " to your mke2fs command. Or use one of the preset types, such as "largefile" or "largefile4" (4MB ratio).
I have a 3TB RAID5 array formatted with ext4 on which I store music and video files, all pretty big files. So I used the preset "largefile4" on it, which specifies an inode-ratio of 4194304 bytes.
I also did some more tweaking on it to decrease journalsize, since I don't need much of it (big files, so little metadata), and reduced reserved space for root with the -m parameter.
But to set basic largefile4, all you need to do is:

mkfs.ext3 -T largefile4 /dev/sdb

Notice it formats way faster than without the largefile4 setting.

You can check out mke2fs settings at /etc/mke2fs.conf. Probably also there on Moblin. Wonder what it's settings are.

Last edited by Ultraman (2010-04-11 18:55:47)

Gullible Jones

Member

Registered: 2004-12-29

Posts: 4,863

Re: Ext3 "fast format"?

Thanks, that worked perfectly!

Edit: Whoops no it didn't, it caused me to run out of space on my drive. Blargh.

Edit again: N/M it was my /boot partition, which I accidentally used largfile4 on. Duh.

Last edited by Gullible Jones (2010-04-12 02:17:32)

Gullible Jones

Member

Registered: 2004-12-29

Posts: 4,863

Re: Ext3 "fast format"?

Update: well that helped, but it wasn't the whole story. Sidux also formats fast, even using "normal" settings. Here's its mke2fs.conf:

[defaults]
    base_features = sparse_super,filetype,resize_inode,dir_index,ext_attr
    blocksize = 4096
    inode_size = 256
    inode_ratio = 16384

[fs_types]
    ext3 = {
        features = has_journal
    }
    ext4 = {
        features = has_journal,extents,huge_file,flex_bg,uninit_bg,dir_nlink,extra_isize
        inode_size = 256
    }
    ext4dev = {
        features = has_journal,extents,huge_file,flex_bg,uninit_bg,dir_nlink,extra_isize
        inode_size = 256
        options = test_fs=1
    }
    small = {
        blocksize = 1024
        inode_size = 128
        inode_ratio = 4096
    }
    floppy = {
        blocksize = 1024
        inode_size = 128
        inode_ratio = 8192
    }
    news = {
        inode_ratio = 4096
    }
    largefile = {
        inode_ratio = 1048576
        blocksize = -1
    }
    largefile4 = {
        inode_ratio = 4194304
        blocksize = -1
    }
    hurd = {
         blocksize = 4096
         inode_size = 128
    }