io operation

[Madhu Sudhan_1]

Hello friends,
How many bytes (maximum), the os can read/write in one single IO operation. How do I find out this ?

Thanks in advance.

[Paula J Frazer-Campbell]

Hi

To be pedantic the system reads in a single operation 1 bit (0 or 1).

Can you explain a little more the information you are looking for?

Paula

[Paula J Frazer-Campbell]

Congrats on you new hat - looks good.

Keep 'em coming.

Paula

[Madhu Sudhan_1]

Thanks. Another way of putting this question that, At one stretch how much it can read ? 1-block or 2-block etc . Like that how many blocks it can read at one go ?

an example,

DB_BLOCK_SIZE of Oracle Databse is DB_BLOCK_SIZE = os_block_size * n

Which is what Oracle gets.

So, in equivalent what is it for the OS.

Thank you.

[Pal Szabo_1]

1. from the
/usr/include/sys/param.h:

Block devices are read in BLKDEV_IOSIZE units. This number must be a power of two and in the range of
DEV_BSIZE <=
BLKDEV_IOSIZE <= MAXBSIZE

DEV_BSIZE=1024
MAXBSIZE=65536
BLKDEV_IOSIZE 2048


And if you make a measurement
on an idle system, with a
writing a large file,
you can check the results
with the sar -d option.

(sar -d options)
r+w/s
Number of data transfers per second (read and writes) from and to the device;
blks/s
Number of bytes transferred (in 512-byte units from
and to the device)


Unfortunately i don't check the results ... :(