Re: Is there something that could change blocksize on iSeries?

Yep. NPIV via VIOS. I participated in configuring the disks on the iSeries
as we moved from P7 to P8 but I don’t remember anywhere to set block size
in SST.

Even if there was, it’s not something that would’ve magically changed block
size from 60k to 90k on a Monday when there were no other changes.

Others have talked about disk segment sizes of 520 for iOS vs 512 of other
OSs but there is not a factor here.



On Fri, Oct 11, 2019 at 7:31 PM Evan Harris <auctionitis@xxxxxxxxx> wrote:

Hi Steve

I would not have thought the block size would have (or could have) been
changed on the i side, but how the disks are connected - native, vscsi or
npiv ?

If it's nip or native I don't think there is even a parameter to set this
unless it is buried somewhere in SST.

Memory tells me you might set some of this when configuring the disk units
in VIOS but it's a while since I have done that and I am no expert - might
give you something to look at or ask about.

We did have some performance issues on a v7k after some firmware updates
that were related to de-duplication capability. Some more patches corrected
that issue - from memory one of the symptoms we identified was an extended
seek time. Might pay to check or ask about that but since you are talking
to the support guys I guess that has already been looked at.


On Sat, Oct 12, 2019 at 11:01 AM Steve McKay <samckay1@xxxxxxxxx> wrote:

The block size in question seems more like it’s the read/write cache

size.

IBM Storage is literally IBM Storage guys that are looking at disk
performance because V9K write times are 3.5 ms. IBM expects write times
closer to 0.5 ms. They are claiming the that “something” changed the

block

size on Sept 16 and that the V9K can’t change the block size so the

system

or application must have changed it.

It seems to me that the SAN would be the only thing that would change

its

block size.

I’ve been on IBM midrange for 30 years and I don’t know of any way for

the

system to change block (cache) size.



On Fri, Oct 11, 2019 at 5:13 PM Vernon Hamberg <vhamberg@xxxxxxxxxxxxxxx

wrote:

I wonder, as well - I just did a quick google on "v9000 block size" -
one hit talked about block size on IBM i disk units is 520 bytes, while
V9000 they are 512 bytes.

Then there is something it called allocation size - we talk about

memory

on IBM i being in blocks of 4096 bytes.

There is also something I don't remember the name, but the amount that
is read from disk - this is up to 128K, IIRC, on IBM i, and this is

used

to reduce I/O by reading the largest "segment" one can.

All in all, that was a lot of words giving no direct answer!! Maybe
it'll trigger some memories.

Vern

On 10/11/2019 3:03 PM, Roberto José Etcheverry Romero wrote:

What do they call block size? You have your pools, your volumes, they

use

extents, etc etc etc, but block size? sounds weird to me... specially

in

such non-binary numbers...

On Fri, Oct 11, 2019 at 12:17 PM Steve McKay <samckay1@xxxxxxxxx>

wrote:

V7R3 system

IBM Storage Support says that the blocksize on our V9000 was changed

from

60K to 90K. They further say that something on the iSeries changed

the

blocksize and there is nothing on the V9K that could change the

blocksize.

Is there anything on the iSeries that can change blocksize?

Thanks,

Steve McKay
(205) 585-8424
samckay1@xxxxxxxxx
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