Re: PowerHA and Journaling

This would be my understanding as well. Journaling change the focus of which pages get written to disk first as the journal receiver data is what is used to recover partial updates in the case of an abnormal shutdown for example.

Also note that just because a dirty page has been written to disk doesn't mean it is discarded from memory, it may still remain in memory for 'some time' especially if it's being accessed.

PowerHA does in fact work at the block level and it cares not what sort of data is in the blocks, if it gets written it gets replicated.

Note that PowerHA works with IBM i doing the replication when you are using internal Power Systems disk and lets the SAN do the replication when you are using SAN storage. It looks the same to the application of course.

- Larry "DrFranken" Bolhuis

www.Frankeni.com
www.iDevCloud.com - Personal Development IBM i timeshare service.
www.iInTheCloud.com - Commercial IBM i Cloud Hosting.

On 3/9/2016 2:28 PM, Charles Wilt wrote:

Not exactly...

The system is constantly flushing changes to objects in memory back to disk
on a page by page basis. When you update a record, the page of memory
containing that record is marked as "dirty". If the page belongs to a
permanent object, at some point the system will update it on disk.

Journalling doesn't cause this. In fact, IIRC for a journaled object, the
system will let the dirty page stay in memory longer. As the journal
receiver pages themselves have a higher priority for getting flushed to
disk.

I don't have my Inside the Dr Soltis books handy to quote the chapter and
verse.

Charles



On Wed, Mar 9, 2016 at 2:02 PM, Stefan Tageson <Stefan.Tageson@xxxxxxxx>
wrote:

Since PowerHA includes implementation of iASP, doesn't matter if you you

use external storage or internal, as long as you migrate the IFS

folders to the iASP, PowerHA will replicate everything in the iASP,

using storage block-page level, so you shouldn't care about journaling.

Please help me understand this. If you are *not* using journaling of your
IFS objects what mechanism will bring your changes down to the surface of
the disk so PowerHA can replicate them? To my knowledge the single level
storage design will try to keep as much hot data as possible in main
storage, and as long as they stay in main storage they will not get
replicated.

Thanks!

Best regards

stefan.tageson@xxxxxxxx
M +46 732 369934

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