Filipe Brandenburger wrote:

Hello,

I noticed something unusual today.

If I "du" a small file (couple of bytes) in CentOS 5, it tells me the file is using 8kb, while I was expecting 4kb which is the block size I'm using.

I tried this on several CentOS 5 machines, both x86_64 and i386:

$ echo test >test.txt $ ls -l test.txt -rw-rw-r-- 1 filbranden filbranden 5 Mar 11 17:24 test.txt $ du -h test.txt 8.0K test.txt

<snip>

I could not find any differences that would explain the behaviour. Have you seen this before? Can you reproduce it on your systems? Do you know how to get the CentOS 4 behaviour?

strange. I don't reproduce on an x86_64 centos 5 machine: [nthierry@localhost ~]$ echo test >test.txt [nthierry@localhost ~]$ ls -l test.txt -rw-rw-r-- 1 nthierry nthierry 5 Mar 11 22:44 test.txt [nthierry@localhost ~]$ du -h test.txt 4.0K test.txt

I'm pretty sure I did nothing special when making the fs.

HTH

Filipe Brandenburger wrote:

Hello,

I noticed something unusual today.

If I "du" a small file (couple of bytes) in CentOS 5, it tells me the file is using 8kb, while I was expecting 4kb which is the block size I'm using.

I tried this on several CentOS 5 machines, both x86_64 and i386:

$ echo test >test.txt $ ls -l test.txt -rw-rw-r-- 1 filbranden filbranden 5 Mar 11 17:24 test.txt $ du -h test.txt 8.0K test.txt

Odd. I'm not seeing this on CentOS 5.2:

$ echo test >test.txt $ ls -ls test.txt 4 -rw-rw-r-- 1 rnichols rnichols 5 Mar 11 16:57 test.txt $ du -h test.txt 4.0K test.txt $ stat test.txt File: `test.txt' Size: 5 Blocks: 8 IO Block: 4096 regular file Device: 341h/833d Inode: 4325491 Links: 1 Access: (0664/-rw-rw-r--) Uid: ( 500/rnichols) Gid: ( 500/rnichols) Access: 2009-03-11 16:57:18.000000000 -0500 Modify: 2009-03-11 16:57:18.000000000 -0500 Change: 2009-03-11 16:57:18.000000000 -0500 $ df . Filesystem 1K-blocks Used Available Use% Mounted on /dev/hdb1 487397840 320075816 142902824 70% /xstore $ su - -c "tune2fs -l /dev/hdb1" | egrep 'features|size' Password: Filesystem features: has_journal resize_inode dir_index filetype needs_recovery sparse_super large_file Block size: 4096 Fragment size: 4096 Inode size: 128

Everything exactly as expected.

Hi,

On Wed, Mar 11, 2009 at 17:29, Filipe Brandenburger filbranden@gmail.com wrote:

If I "du" a small file (couple of bytes) in CentOS 5, it tells me the file is using 8kb, while I was expecting 4kb which is the block size I'm using.

Found it! It's not related to CentOS 4 or 5 (I found a C4 machine in which small files took 8kb of diskspace and a C5 machine in which small files took 4kb). It's related to SELinux being enabled or not. Casually most of my C4 machines had SELinux disabled and most of my C5 have it enabled. Now I dug out some machines with the opposite config and I checked it out.

I believe if SELinux is enabled, it will use extended attributes to store the file's SELinux context (you can see it with "ls -Z", for some reason you cannot see it with "getfattr -d", I was expecting that to be possible). I guess when the file has extended attributes it will use an additional block to store them. That basically doubles the storage requirements if you have millions of tiny files...

ACLs would probably have the same effect (I did not test it though).

I wonder if there is a way to override this, for instance by mounting a filesystem and disabling extended attributes, specifying the SELinux context for all the files in the mount options or something. I know that is possible for NFS, but not for local filesystems... I'll dig in, I'll let you know if I find anything.

Thanks! Filipe