Re: Exadata writeback Flash Cache usable space

I do not think that this is necessarily the case.

The flashcache mode being set to "WriteBack" should not reduce the capacity of the flash cache available by a third. Also - I do not think that there's a dependency or link between the redundancy of the ASM disk groups and the flashcache mode.

Each HC cell is provisioned with 25.6 TB of "raw" PCI flash...

From an environment that has "WriteBack Flash Cache Enabled" - I see a reported cache size of 23 odd TB for each cell (this is an X8M-2)

# cellcli -e list flashcache detail
effectiveCacheSize: 23.28692626953125T
id:
size: 23.28692626953125T
status: normal

Additions, comments, corrections are welcome.

Thanks,

--Rajesh

On Sat, Jul 17, 2021 at 4:22 AM Ls Cheng <exriscer_at_gmail.com> wrote:

> Hi
>
> We are deploying a new Exadata x9m quarter rack with HC disks next week
> and the flashcache will be configured using writeback instead of
> writethrough.
>
> In writeback mode the flash is mirrored whereas in writethrough if I
> understood correctly there is no mirroring. So I have a doubt, the quarter
> rack has 76.8 TB raw flash space, what is the usable space with writeback
> enabled? Since we are using High Redundancy I expect 25.6TB usable flash
> cache space, correct?
>
> Thanks
>
>
>

--
http://www.freelists.org/webpage/oracle-l