Disk Block Size

Hi All

I am doing some sizing work to attempt to quantify the effect of replacing
internal disks with SAN backed storage. Basically we want to quantify the
IO on the i and then model that using SAN sizing tools (e.g. Disk Magic)

One of the question is have been asked is what Block Size does the IBM i
use ? This appears to be something of a loaded question, as it seems to
depend on what context the term block size is used in. Could also be that I
just don;t understand...

The closes I have come to an authoritative answer yet is this quote:

" Paging of the objests (sic) in this virtual address space is performed in
4 KB pages. However, data is usually blocked and transferred to storage
devices in bigger than 4 KB blocks. Blocking of transferred data is based
on many factors, for example, expert cache usage."

from this document "Hints and Tips for implementing Storwize and IBM
FlashSystems in an IBM i environment"

I have not been able to find any references telling me what the factors
that influence blocking are or what block sizes would be used in those
cases.

4K seems a bit small for the block size but so far I have not been able to
come up with anything more exact.

So what is the block size used in a read or write operation on an IBM disk ?

For a bit of further information we are thinking about using the blocks
size together with the read and write numbers in the QAPMDISK file (columns
DSDROP and DSDWOP) so perhaps that makes a difference in what block size we
should use for the calculations.

Any opinions and discussion welcome.