[plug] Missing storage space

[Matt Kemner]

Hi Jim

> The numbers df gives me for it do not appear consistent.  I get
> /dev/sda1  245409  2062  230676  1%  /media/removable
>
> Now I expect the 245409 since manufacturers and computers use different
> definitions of MB.  However I would expect total to equal used +
> available.  What happened to the missing 12671 blocks?  Filesystem
> overhead perhaps?

You don't say which file system you are using, but most *nix type file
systems reserve a small percentage of blocks for super-user access only
(5% for ext2 and ext3) - once you hit that magical 95% limit the blocks
available will be 0, but root will still be able to write to the disk
until the used blocks matches the total.

This is for historical reasons - it prevented a user from filling up the
drive and causing catastrophic failures for daemons not written to handle
low-disk-space situations - and in some cases even preventing the sysadmin
from logging in to fix it.

If you are using ext[23] then you can adjust the reserved blocks count
with the -m [reserved-blocks-percentage] or -r [reserved-blocks-count] flags.

 - Matt