Re: Question on Exadata X8 - IO

Seeing in below doc which state its recommended to go for high redundancy ASM disk group(i.e. triple mirroring) in case we are using write back flash cache as because the data will be first written/stay in flash cache and flushed to the disk later stage and in case of failure it has to be recovered from mirror copy. But i am wondering , is this not possible with double mirroring , will it not survive the data loss in case of failure? Want to understand what is the suggested setup which will give optimal space usage without compromising IOPS and data loss.

https://docs.oracle.com/en/engineered-systems/exadata-database-machine/sagug/exadata-storage-server-software-introduction.html#GUID-E10F7A58-2B07-472D-BF31-28D6D0201D53

Regards
Lok

On Fri, Feb 12, 2021 at 10:42 AM Lok P <loknath.73_at_gmail.com> wrote:

> Hello Listers, We are moving from exadata X5 to X8 and there are multiple
> reasons behind it. Few of them are , 1)we are almost going to saturate the
> existing storage capacity(DB size reaching ~150TB) in current X5. 2)And the
> current IOPS on X5 is also reaching its max while the system works during
> its peak load.
>
> We are currently having HIGH redundancy(triple mirroring) for our existing
> X5 machines for DATA and RECO disk group and DBFS is kept as NORMAL
> redundancy(double mirroring). Now few folks raised questions on the impact
> on IOPS and storage space consumption, if we use double mirroring(NORMAl
> redundancy) vs triple mirroring(High redundancy) in the new X8 machine. I
> can see the benefit of double mirroring(Normal redundancy) being saved in
> storage space(around 1/3rd in terms of DATA and REDO copies), but then what
> is the risk wrt data loss, is it okay in a production system? (Note- We do
> use ZDLRA backup for taking the DB backup. And for disaster recovery we
> have active data guard physical standby in place which runs in read only
> mode).
>
> With regards to IOPS, we are going with default write back flash cache
> enabled here. Is it correct that with double mirroring we have to
> write/read into two places VS in triple mirroring we have to do that in
> three places , so there will also be degradation in IOPS with triple
> mirroring/High redundancy as compared to double mirroring? if it's true
> then by what percentage the IOPS degradation will be there? And then if
> it's okay if we go for double mirroring as that will benefit us wrt IOPS
> and also saves a good amount of storage space?
>
> Regards
>
> Lok
>

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