topic Re: block size per write in Operating System - HP-UX

block size per write

Eric Hess — Tue, 15 Oct 2002 15:35:54 GMT

How can I determine what my block size is per write to disk on the O/S

Re: block size per write

harry d brown jr — Tue, 15 Oct 2002 16:03:08 GMT

What are you using to write??

live free or die
harry

Re: block size per write

A. Clay Stephenson — Tue, 15 Oct 2002 18:14:21 GMT

The size of writes is governed by the application and specifically by the nbytes parameter to the read() system call. This parameter can vary from write() to write(). One of the best ways is to install tusc.
http://gatekeep.cs.utah.edu/hppd/hpux/Sysadmin/tusc-7.3/

Tusc will allow you to trace system calls and actually see the values passed to the system calls. That will enable you to get an exact answer.

Re: block size per write

Sridhar Bhaskarla — Tue, 15 Oct 2002 18:32:26 GMT

Hi Eric,

It really depends on your application. There are two kinds of block sizes - File system block size and the physical disk block size (512 bytes or a sector). Physical disk block size is masked by the File system block size.
I believe you meant IO size.

The IO size is dependent on random, sequential, synchronous and asynchronous, discovered direct etc., Applications like Oracle can give a good picture of it's IO.

One of the major advantages of having VxVM against LVM is that it provides a utility called "vxtrace" that can be used to determine the type and size of IO. Unless you have VxVM or you know how your application writes, it is not possible to determine the IO details.

-Sri

Re: block size per write

Sanjeev Kohli_1 — Wed, 16 Oct 2002 04:43:17 GMT

Hi Eric

U can get the filesystem block size by typing the command
fstyp -v /dev/vg##/lvol# .
By this command u will come to know what is the filesystem block size .
Actually in HP-UX allocation is on a random basis depending on the size of data being written on to the disk.

Sanjeev