Writing to disk

[Dan Bonham]

I need to find out what is the smallest size block that is written to disk. That is the default size, we are running 11.0.

TIA

Rusty

[Joseph C. Denman · Accepted solution]

I believe 1K block size is the default. To find out what yours is, do this:

fstyp -v /dev/vg01/lvol1

#note the f_bsize

...jcd...

[Dan Bonham]

Mine reports 8192 for f_bsize.
so, even if I have a smaller file that 8k, it will still take up 8k on the disk.

is that true?

Rusty

[James R. Ferguson]

Hi Rusty;

Knowledge Base doucment #1100330242 notes that for VxFS filesystems, 'v_bsize' represents the largest possible block size which is 8K. 'f_bsize' (at returned too, with 'fstyp -v') is known as the "fragment size" but represents the actual block size (usually 1K).

In point of fact, if you create a small file ('echo x > /tmp/smallfile') and then do a 'du /tmp/smallfile', you will note that the size of the file is "2" 512-byte blocks, or 1K.

Regards!

...JRF...

[Dan Bonham]

James,
here is the output from my fstyp command. I do not see a v_size.

vxfs
version: 3
f_bsize: 8192
f_frsize: 1024
f_blocks: 512000
f_bfree: 309341
f_bavail: 309341
f_files: 8192
f_ffree: 1073792296
f_favail: 1073792296
f_fsid: 1073741828
f_basetype: vxfs
f_namemax: 254
f_magic: a501fcf5
f_featurebits: 0
f_flag: 0
f_fsindex: 6
f_size: 512000

Which on is telling me the smalles size that is written to disk.

thanks,

Rusty

[linuxfan]

Hi Rusty,

what James meant f_frsize (fragment size)

Here is the document James was talking about

/Begin/
To determine the current block size for the vxfs file system:

fstyp -v /dev/vg00/lvol#

For example:

# fstyp -v /dev/vg00/lvol1

f_bsize: 8192

Note: The f_bsize parameter reports the block size for the vxfs
file system.


To determine the current block size for the hfs file system:

tunefs -v /dev/vg00/rlvol# | grep bsize

For example:

# tunefs -v /dev/vg00/rlvol4 | grep bsize

sbsize 2048 cgsize 2048 cgoffset 24 cgmask 0xfffffff8
bsize 8192 bshift 13 bmask 0xffffe000

Here is an example of how HFS and VxFS actually interpret these fields:

Field HFS Value for VxFS
----- --- --------------
f_bsize block size (8K) largest possible block size (8K)
f_frsize fragment size (1K) actual block size (usually 1K)

/End/


So the the smallest block size you can write is 1K (1024)

-HTH
Ramesh

[Sridhar Bhaskarla]

Your smallest size is your f_frsize. 8K is the max I/O can can be produced on the system.

-Sri

[James R. Ferguson]

Hi (again) Rusty:

Ah, I just can't type! The value from 'fstyp -v' that I was referring to is 'f_frsize'. You should see it immediately below 'f_bsize'.

Regards!

...JRF...

[Dan Bonham]

Thanks guys for your help.

I have a good understanding now.

Does anybody happen to know how to find the same information (block and fragment) on an AIX box?

Thanks again,

Rusty

[Bill Hassell]

Another way to locate the block and frag sizes is to use: df -g /mount_point

Or you can use the latest version of bdfmegs which now has a -v option to show block/frag size, filesystem type and whether it supports largefiles. This script always produces 1-line per mountpoint regardless of length. Download a copy from:

ftp://contrib:9unsupp8@hprc.external.hp.com/sysadmin/coolscripts/

Note the ftp:, not http. Also, for IE 5.0 users, there is a bug which causes a hang when looking at ftp sites. Change the "Enable folder view in FTP" to disabled (Tools-> Internet-> Advanced)

Or use plain old ftp to the hprc machine, login is contrib, pw=9unsupp8