7. Formatting an ext2/3 partition
When a hard drive is partitioned, it is mapped into sections, but
the sections are empty. It is like a newly constructed library;
shelves, signs, and a card catalogue system must be put in place
before the books are put away.
The organizational structure inside a partition is called a file
system. With Linux, the standard file system is ext2 and ext3. The
ext3 file system is ext2, plus a log of disk writes called a
journal. The journal allows the system to recover quickly from
accidental power outages, among other things.
The principal tool for making an ext2/3 file system in a partition
is mke2fs. It is usually found in /sbin. mkfs.ext2 and
mkfs.ext3 are frontends which pass specific
options to mke2fs.
.1. Simple Invocation
mke2fs /dev/hdb1
mkfs.ext2 /dev/hdb1
both of which make an ext2 file system on the first partition of the second drive, and
mke2fs -j /dev/hdb1
mkfs.ext3 /dev/hdb1
make an ext3 file system.
.2. Reserved blocks
The -m option is probably the one of most use to non-experts. If the
file system becomes filled and there is no more space to write, it
is basically unusable because the operating system is constantly
writing to disk. By default, five percent of the partition is
reserved for use by the root user. This allows root to conduct
administrative activities on the partition and perhaps move some
data off. However, this is most critical when the partition contains
/ or home directories. For pure data partitions, this is just lost
space. Five percent of a 250Gb partition is 12.5 Gb. Especially in
the case of large partitions, it is safe to set the reserved space
to the minimum, which is one percent.
mkfs.ext3 -m 1/dev/hdb1
creates a file system with only 1% of its space reserved for the
root user. tune2fs -m can be used to adjust the reserved blocks
after data is loaded on the partition.
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