Disk space usage increased after move to other drive.

stefaandk · 06-18-2006, 11:38 PM

I might be off the mark here but how can I determine the block size of my disk.

I moved a directory from a RH9 to a FC4 machine and on the FC4 machine the same dir and files are using 27 megs more then on the old one.

Both are using ext3 file systems, both give this resulting from an fdisk -l
Units = cylinders of 16065 * 512 = 8225280 bytes

If its not block size can it be anything else that could cause this difference in disk usage?

Thanks,

jlliagre · 06-19-2006, 03:53 PM

Maybe sparse files (not sure if ext3fs support them though).

fsbooks · 06-19-2006, 05:08 PM

Did you "move" or "copy"? One way to compare would be to do a du -sk on all the files and then compare. i.e. find . -type f|while read f;do du -sk "$f";done >dusk.out

Blocksize can be found (as root) with tune2fs <device>.

Sparse files could lead to an increase in filesize (re jlliagre), as could symbolic links copying the referent files or hard links losing the links. rsync at least has flags for all these potentialities (-S;-l;-H).

stefaandk · 06-19-2006, 06:12 PM

It's actually being copied through Plesk which is a hosting package, there is a migration tool in there that copies everything from one server to another.

The end result is simply the same dirs with the same file with the same permissions, but still there is an extra 27 megs there.

What are sparse files?

jlliagre · 06-20-2006, 12:59 AM

Sparse files are files containing "holes". The system returns nulls (zeroes) when data is read from these holes.

Here's an example of creating such a file (made on Solaris and UFS):

Code:

$ mkdir sparse
$ cd sparse
$ du -k .
1
$ df -k .
Filesystem            kbytes    used   avail capacity  Mounted on
/dev/dsk/c0d0p4      14421267 11763104 2513951    83%    /mnt/p4
$ dd if=/dev/zero of=sparse bs=1024k seek=1024 count=1
1+0 records in
1+0 records out
ls -l
total 2112
-rw-r--r--   1 jlliagre jlliagre 1074790400 Jun 20 07:52 sparse
$ du -k .
1057    .
$ df -k .
Filesystem            kbytes    used   avail capacity  Mounted on
/dev/dsk/c0d0p4      14421267 11764161 2512894    83%    /mnt/p4

The created file reports a size of 1 gigabyte, but use only a little more than 1 kilobyte.
If you copy or backup this file with tar, the result won't be sparse, so much bigger.